Windows Update Error 0x80073701 — What It Means & How to Fix It

What Does This Error Mean?

Windows Update error 0x80073701 means 'The referenced assembly could not be found.' Windows tried to install an update that depends on a specific component assembly, but that assembly is missing from your system. This happens when a previous update removed or corrupted a component that a new update depends on. DISM repair usually fixes this.

Affected Models

Windows 10
Windows 11
Windows 8.1

Common Causes

A component assembly that the update depends on was removed or corrupted by a previous failed update
A third-party system cleanup tool aggressively removed files from the WinSxS folder, deleting required assemblies
The Windows component store has orphaned references to assemblies that are no longer present
A Windows feature was forcibly removed in a way that deleted shared assemblies needed by other components
Disk errors caused assembly files to become unreadable or partially corrupted

How to Fix It

Run DISM to restore missing assemblies. Open Command Prompt as Administrator and type: DISM /Online /Cleanup-Image /RestoreHealth — then press Enter. DISM specifically re-downloads and reinstalls missing component assemblies from Microsoft's servers.

This is the most direct fix for a missing assembly error. The process takes 10 to 30 minutes and requires an internet connection. Restart your PC after it completes.
Run System File Checker. After DISM completes, type: sfc /scannow — then press Enter. SFC checks for and replaces system files that reference the missing assemblies, ensuring all components are properly linked.

SFC and DISM complement each other. Run both, in that order. After both complete, restart and try Windows Update again.
Check if a system cleanup tool has been used recently. Tools like CCleaner, Wise Disk Cleaner, and similar programs have options that can delete WinSxS folder contents — which breaks Windows assemblies. If you used one, stop using the WinSxS cleanup feature and run DISM to recover.

Never use third-party cleanup tools on the WinSxS folder. Windows manages this folder itself and knows what is safe to remove. Third-party tools can delete assemblies that Windows Update depends on.
Perform a Windows in-place upgrade repair if DISM cannot fix the missing assembly. Download the Windows Media Creation Tool from microsoft.com. Run it, choose 'Upgrade this PC now,' select 'Keep personal files and apps.' This reinstalls all Windows components from scratch.

An in-place upgrade is the most thorough repair option short of a full reinstall. It replaces every Windows system file including all component assemblies while keeping your files and settings.
Try installing the update manually from the Microsoft Update Catalog. Go to catalog.update.microsoft.com and search for the failing update's KB number. Download and run the standalone installer. The standalone installer sometimes handles missing dependencies differently than the Windows Update service.

The standalone update installer has its own dependency handling that can resolve missing assembly issues that block the automatic Windows Update process.

When to Call a Professional

If all DISM and SFC repairs fail and the in-place upgrade is not available on your PC, a technician can perform a clean Windows installation while preserving personal files, which fully rebuilds the component store.

Frequently Asked Questions

What is a component assembly?

In Windows, an 'assembly' is a package of related files that work together as a unit — similar to a library in programming. For example, the .NET Framework is made up of many assemblies. When an update requires a specific assembly and that assembly is missing, the update cannot install. Assemblies are stored in the WinSxS folder and tracked by the Windows component store. DISM can re-download and register missing assemblies.

Can I find out which specific assembly is missing?

Yes — open C:\Windows\Logs\CBS\CBS.log in Notepad and search for '0x80073701' or 'assembly not found.' The lines near those entries will show the exact assembly name that is missing. You can then search for that assembly name online to understand which Windows feature or component it belongs to. This helps determine whether you need to repair or reinstall a specific Windows feature.

I ran DISM but the error persists. What next?

If DISM reports it successfully restored the component store but the update still fails, try downloading the update manually from the Microsoft Update Catalog. If that also fails, the assembly may belong to a specific Windows feature that needs to be toggled — turn the feature off in 'Turn Windows features on or off,' restart, then turn it back on. As a last resort, the in-place upgrade repair reinstalls all assemblies from scratch.