How to fix File System Error (-1073741521) in Windows?

File system error (-1073741521) appears when you open Command Prompt, Task Manager, an installer or an Office file. It is the Windows code 0xC000012F: a program or library file Windows tried to load is not a valid program any more, so it is damaged. Repair the disk and Windows files from the recovery screen first.

Facts checked on 15 October 2026. Steps written for Windows 11 (25H2 and 26H2) and Windows 10 22H2.

What File system error (-1073741521) means

You start Command Prompt as administrator, open Task Manager, run an installer or open a Word document. Instead of the program, Windows shows a box with the program's path and the line File system error (-1073741521). In the Microsoft Q&A thread on this error, the user could not run anything with administrator rights, and Office programs also said that MSIMG32.dll was missing, although the file was in its place.

The number is a Windows status code written as a negative decimal. In hex, -1073741521 is 0xC000012F. Microsoft's list of NTSTATUS values names it STATUS_INVALID_IMAGE_NOT_MZ, with the text "The specified image file did not have the correct format: it did not have an initial MZ."

Because every program started with administrator rights can fail at once, the damaged file is often part of Windows itself, not the program named in the box. The usual advice, "open Command Prompt as administrator and run SFC", then fails with the same box. The fixes below run from the recovery screen or Safe Mode instead.

Why the file system error -1073741521 appears

The code says a program file is not a valid program. Rank the reasons like this and start at the top.

How to fix File System Error (-1073741521) in Windows

Fix 1 repairs the disk and system files from the recovery screen and helps most readers. Fix 2 finishes the repair with DISM when SFC cannot. Fix 3 is for readers whose error comes from Word or one app. Fixes 4 to 6 undo recent changes and rule out malware, and Fix 7 reinstalls Windows while keeping your files and apps.

Fix 1. Check the disk and repair system files from the recovery Command Prompt

20 to 40 minutesLow riskEveryone, first. It works even when no program opens with administrator rights inside Windows.

The code means a program file is damaged. CHKDSK fixes the file system errors that damage files, and SFC then replaces damaged Windows files with good copies. The recovery Command Prompt already has full rights, so the broken administrator prompt is not used.

1. Select Start > Power, hold Shift and select Restart. This needs no administrator rights.
2. Select Troubleshoot > Advanced options > Command Prompt. Pick your account and type its password. If Windows asks for the BitLocker recovery key, enter it.
3. Type dir C:\Windows and press Enter. If it lists files, Windows is on C:. If not, try D: and use that letter below.
4. Run chkdsk C: /f and wait until it finishes.
5. Run the offline system file check (command below) and wait until it reaches 100 %.
6. Type exit, select Continue to start Windows, and open Command Prompt as administrator to test.

Offline system file check (recovery Command Prompt)

sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows

What the SFC messages mean: Run DISM and SFC to repair Windows system files More about CHKDSK and how to read its result: Check a disk for errors (chkdsk)

Fix 2. Run DISM and SFC in Safe Mode with Networking

30 to 60 minutesLow riskSFC in Fix 1 found damaged files but could not repair some of them.

SFC copies good files from the Windows component store, and when that store is damaged too, SFC cannot finish. DISM repairs the store, but it needs a source. In the Microsoft Q&A thread, DISM in recovery failed because it found no source, and it worked once it could reach Windows Update. Safe Mode with Networking gives it that connection.

1. Select Start > Power, hold Shift and select Restart.
2. Select Troubleshoot > Advanced options > Startup Settings > Restart.
3. Press 5 or F5 for Enable Safe Mode with Networking and sign in. Check that the PC is online.
4. Select Start, type cmd, right-click Command Prompt and select Run as administrator.
5. Run DISM /Online /Cleanup-Image /RestoreHealth and wait until it reaches 100 %. It can pause at 20 % or 62 % for a while.
6. Run sfc /scannow and wait until it finishes.
7. Restart normally and test the program that showed the box.

Fix 3. Repair Microsoft Office or the one app that shows the error

10 to 30 minutesLow riskOnly Word, another Office program or one app shows the box, or an Office program says a DLL such as MSIMG32.dll is missing.

When other programs start fine, the damaged file most likely belongs to that one app. A repair replaces the app's own program files. Run Fix 1 first, because a missing-DLL message from Office can also point to a damaged Windows file, as in the Q&A thread.

1. Press Win + I and open Apps > Installed apps.
2. Find Microsoft 365 or Microsoft Office, select the three dots and then Modify.
3. Choose Quick Repair and select Repair. Close all Office programs when asked.
4. Open the Word document again.
5. If the box is still there, run the repair again with Online Repair, which reinstalls Office.
6. For another app, select it in Installed apps, then Advanced options > Repair, or uninstall it and install the latest version from its maker.

Office repair step by step: How to repair Microsoft 365 or Office Repairing other apps: How to repair or reset an app in Windows

Fix 4. Remove the latest Windows update from the recovery screen

15 minutesLow riskThe error started right after Windows installed an update.

An update that stopped halfway can leave Windows files partly written, so they no longer start with a valid header. Removing an update in Settings needs administrator rights, which this error blocks. The recovery screen removes the latest update without that prompt.

1. Select Start > Power, hold Shift and select Restart.
2. Select Troubleshoot > Advanced options > Uninstall Updates.
3. Select Uninstall latest quality update first. Use Uninstall latest feature update only if a version upgrade came just before the error.
4. Sign in with your account when asked and confirm.
5. Let the PC restart and test the program that showed the box.

Fix 5. Roll Windows back with System Restore from the recovery screen

20 minutesRead the warningSystem Restore was on before the error began and Fixes 1 to 4 did not help.

A restore point puts Windows system files, settings and drivers back to a day before the files were damaged. Opening System Restore inside Windows needs administrator rights, so start it from the recovery screen.

1. Select Start > Power, hold Shift and select Restart.
2. Select Troubleshoot > Advanced options > System Restore and sign in.
3. Choose a restore point from before the error started and select Next.
4. Select Finish and wait. Do not turn the PC off.
5. After the restart, test the program that showed the box.

More on restore points: Undo recent changes with System Restore

Fix 6. Scan for malware with Microsoft Defender, including the offline scan

15 minutes to 2 hoursLow riskMany unrelated programs fail, the error appeared with no update or crash before it, or Defender already showed a warning.

Some malware overwrites or replaces program files, which leaves them without a valid header. We could not confirm a specific malware family tied to this code, so treat this as a check, not the main fix. The offline scan runs before Windows loads, so it does not need the administrator prompt that fails.

1. Select Start, type Windows Security and open the app.
2. Select Virus & threat protection > Scan options.
3. Select Full scan and Scan now, and wait until it finishes.
4. If the full scan fails or finds nothing, go back to Scan options, choose the offline scan and select Scan now. The PC restarts and scans for about 15 minutes.
5. Open Protection history to see what was found and removed.
6. Run Fix 1 again afterwards, because removing malware does not repair the files it damaged.

Full steps and how to read the results: How to scan for malware with Microsoft Defender

Fix 7. Reinstall Windows while keeping your files and apps

1 to 2 hoursRead the warningFixes 1 to 6 did not help, or SFC and DISM could not repair every file.

A repair install replaces every Windows file, including the damaged program and DLL files SFC could not reach, and keeps your apps, settings and files. In the Q&A thread, the user planned a refresh of the install because SFC still found errors after DISM.

1. On Windows 11, open Settings > System > Recovery and select Reinstall now next to Fix problems using Windows Update.
2. If that option is missing or fails, download the Windows ISO from Microsoft's official download page, double-click it to mount it and run setup.exe.
3. Choose Keep personal files and apps when setup asks what to keep, and start the install.
4. If setup shows the same File system error box, restart with Shift + Restart and use Troubleshoot > Reset this PC > Keep my files. This keeps your files but removes installed apps.
5. After Windows starts, test the program that showed the box.

Full steps for both routes: Reinstall Windows without losing files

If the file system error -1073741521 is still there

Three logs tell you what the repairs found. Read them before you contact support.

1. Press Win + R, type eventvwr.msc and press Enter.
2. Open Windows Logs > Application and filter by the sources Chkdsk and Wininit to read the CHKDSK result.
3. Open C:\Windows\Logs\CBS\CBS.log and search for lines with [SR] to see which files SFC could not repair.
4. Open C:\Windows\Logs\DISM\dism.log and look at the last lines for the reason DISM stopped, such as a missing source.
5. If CHKDSK reports bad sectors, or the same files stay damaged after Fix 7, suspect the drive.

• What to send to support: the full message with the path, the CHKDSK, SFC and DISM results, the Windows version from Settings > System > About, and what Fixes 1 to 7 showed.
• Where to ask: Microsoft Q&A or Microsoft Support when the damaged files are part of Windows, or the app's maker when only its files are named.
• When it is not software: clicking noises, very slow copying, bad sectors or files that change by themselves point to a failing drive. Back up and replace the drive; no Windows repair fixes that.
• If the PC also freezes or shows blue screens: test the memory, since bad RAM can damage files as they are written: How to test your RAM with Windows Memory Diagnostic

How to keep program files from being damaged again

Windows 10 left support on 14 October 2025. The fixes above work the same on Windows 10 22H2, but it no longer gets most security and repair updates, so an upgrade to Windows 11 is the lasting route.

Frequently asked questions

What is File system error (-1073741521)?

It is the Windows status code 0xC000012F, written as a negative decimal number. Microsoft names it STATUS_INVALID_IMAGE_NOT_MZ: the program or DLL file Windows tried to load did not start with the MZ mark every Windows program has. In practice the file is damaged, overwritten or empty. When many programs fail, the file is most likely part of Windows. Start with Fix 1: CHKDSK and SFC from the recovery screen.

Why do I get it when I open a Word document?

Because opening the document starts Word, and Word loads its own files and many Windows DLL files. If one of them is damaged, Word cannot start and Windows shows the box. If other programs work, repair Office first with Quick Repair, then Online Repair (Fix 3). If Command Prompt or Task Manager fail too, the damaged file is in Windows, so begin with Fix 1.

Why does Office say MSIMG32.dll is missing when the file is there?

The message is misleading. Windows found the file but could not load it because its content is damaged, and Office reports that as missing. That is what this code means. In the Microsoft Q&A thread on this error, the DLL was in its place and the problem went away after DISM and SFC repaired Windows files. Do not download a replacement DLL from a website; run Fix 1 and Fix 2 instead.

Why can't I open Command Prompt or Task Manager?

Because they start with administrator rights, and in the reports we read every elevated program failed at once while some normal programs still ran. The damaged file is shared by all of them. That is why Fix 1 runs from the recovery Command Prompt, which already has full rights, and Fix 2 runs from Safe Mode with Networking.

Is lowering User Account Control a safe way around it?

No, not as a fix. In the Microsoft Q&A thread, one user turned UAC off in Safe Mode so that DISM could run, then turned it back on after the repair. It worked for that user, but it removes a key protection, and a PC with damaged program files is exactly where you want it. Use the recovery screen and Safe Mode with Networking (Fixes 1 and 2), and the repair install (Fix 7) if they fail.

Is my hard drive failing?

Usually not, but it is possible. Damaged files most often follow a crash, a power cut or an update that stopped halfway. A failing drive shows other signs too: clicking noises, very slow copying, files that change by themselves, or CHKDSK reporting bad sectors. If you see those, back up your files at once and check the drive before you spend time on Windows repairs.

What is File system error (-1073741515)?

It is a different code. In hex, -1073741515 is 0xC0000135, which Microsoft's list names STATUS_DLL_NOT_FOUND: the program could not start because a DLL file it needs was not found. Reinstalling the program that shows it often helps, and Microsoft's own text says so. If many programs show it at once, run Fix 1 on this page, because a damaged Windows install can cause both codes.

Does this error happen on Windows 11 and Windows 10?

Yes. The Microsoft Q&A thread about this message comes from Windows 10, and the code means the same on Windows 11. The fixes are the same on both. Only one path differs: Reinstall now in Settings > System > Recovery exists on Windows 11, while on Windows 10 you start the repair install from the Windows ISO. Readers searching in Russian for "11 виндовс" (Windows 11) will find the same steps apply.

Will a repair install delete my files?

No, when you choose Keep personal files and apps. Setup replaces Windows files and keeps your documents, settings and installed programs. Reset this PC with Keep my files also keeps your documents but removes installed apps, so you reinstall them afterwards. Back up your important files first in either case, because a power cut or a failing drive during setup can still cause loss.