How to Fix Windows Update Error 0x80073701

By ErrorFix · Updated October 23, 2026 · 8 min read

What error 0x80073701 means

Break the code apart and it tells its own story. 0x80073701 is an HRESULT: severity FAILURE, facility WIN32, code 0x3701. That last part maps to a Windows constant called ERROR_SXS_ASSEMBLY_MISSING, whose official description reads "The referenced assembly could not be found." In plain terms, Windows keeps a central library of every system component — the component store, tucked away in the WinSxS folder — and every update and feature installation is assembled from pieces of that library. Error 0x80073701 fires when the servicing stack reaches for a piece that should be in the library and comes up empty.

It most often appears while a cumulative update is installing, and it is equally common when you try to turn on a Windows feature or install a server role. The damaged piece is usually not something you deleted on purpose — these things break during interrupted updates, sudden power cuts mid-install, disk problems, or one half-installed package confusing the servicing stack about what is actually present. The good news: because the missing piece lives in the repair tools' reach, this error has one of the highest fix rates of any Windows Update code.

Common causes

• Component store corruption: the WinSxS store has damaged or incomplete files, so the servicing stack cannot find the assembly the update expects — the number-one cause.
• An update interrupted mid-install: a power cut, forced shutdown, or reboot during an update can leave packages half-applied and the store's bookkeeping wrong about what is actually on disk.
• Stuck superseded packages: old updates that should have been cleaned up linger in the servicing stack and confuse the assembly resolution of the new update.
• Missing optional features or language packs: updates sometimes reference language packs or optional features that were removed from the system, so their assemblies genuinely do not exist anymore.
• Disk errors or bad sectors: a drive with file-system damage can quietly corrupt the component files an update needs, producing a missing-assembly error on an otherwise healthy system.

How to fix error 0x80073701 — step by step

Work through these fixes in order. Step 2 repairs the underlying damage in most cases; steps 3 and 4 give you alternative ways to get the update on; step 5 hunts down the exact broken package; step 6 is the full rebuild when nothing else sticks.

1. Restart your PC and retry the update once. Save your work and restart the PC with a real restart, not a shutdown, since shutdown can hibernate the session and skip the full reset of system services. After logging back in, open Settings, go to Windows Update, and click Check for updates to give the failed update one clean attempt. A simple restart clears transient servicing locks and occasionally lets the update finish without any further work.
2. Repair the component store with DISM and SFC. Right-click the Start button and open Terminal (Admin) or Command Prompt (Admin). Run DISM /Online /Cleanup-Image /StartComponentCleanup first to tidy the component store, then DISM /Online /Cleanup-Image /RestoreHealth to repair corruption against Windows Update. When that completes, run sfc /scannow to check protected system files. Restart afterward. This one-two punch fixes 0x80073701 whenever the missing assembly is simply a corrupt or incomplete component.
3. Install the failing update from the Microsoft Update Catalog. Open Settings, go to Windows Update, then Update history, and write down the KB number of the update that fails with 0x80073701. Visit catalog.update.microsoft.com, search that KB number, and download the package matching your system, x64 for most PCs, ARM64 for Snapdragon devices. Double-click the downloaded MSU file to install it directly. The catalog installer applies the update through a different path than the automatic update agent, and it frequently succeeds where the automatic path keeps failing.
4. Inject the update package manually with DISM. Create a folder such as C:\Temp\KB and download the failing update as an MSU from the Microsoft Update Catalog into it. Open Terminal (Admin) and extract the CAB with expand -F:* C:\Temp\KB\*.msu C:\Temp\KB\, then inject it with DISM /Online /Add-Package /PackagePath:C:\Temp\KB\, pointing at the extracted CAB file by its full name. This hands the package directly to the servicing stack and bypasses whatever metadata mismatch was stopping Windows Update.
5. Find the broken package in the CBS log and clear it. Open C:\Windows\Logs\CBS\CBS.log in Notepad and search for ERROR_SXS_ASSEMBLY_MISSING to see exactly which KB package failed. If a specific update keeps being offered and failing, you can hide that problem package so servicing ignores it: in the registry at HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Component Based Servicing, take ownership of the package key, set its CurrentState value to 0, and restore the original permissions before restarting. Then run Windows Update again.
6. Run an in-place upgrade as a last resort. Download the Media Creation Tool from Microsoft's website and create a current Windows 10 or Windows 11 installation ISO matching your edition. Mount the ISO, run setup.exe, and choose Keep personal files and apps. This reinstalls Windows over itself, rebuilding the entire component store from scratch, and it is the reliable fix when the CBS log shows missing assemblies scattered across many different packages.

Did this fix it? Quick checklist

• PC restarted with a full restart, and the update retried from a clean boot
• DISM component cleanup and RestoreHealth plus SFC completed with no remaining corruption
• Update installed from the Microsoft Update Catalog, or the CAB injected manually with DISM
• The broken package identified in the CBS log and cleared from the servicing queue

If 0x80073701 survives every step, the corruption may sit in the hard drive itself rather than the files. Open an elevated Command Prompt and run chkdsk C: /f /r, let it scan on the next restart, and then re-run DISM. A drive that keeps corrupting system files will keep producing missing-assembly errors until the underlying disk problem is fixed.