How to Fix KB5065426 Error 0x800f0991 (Step-by-Step)

If KB5065426 fails to install on your Windows 11 PC, you’re not alone.

Many users are seeing:

• Error 0x800f0991
• Update fails halfway
• “Retry” loops
• Update installs but fails again after reboot

👉 The good news:
You can fix this without reinstalling Windows in most cases.

This guide shows simple, working solutions you can follow step by step.

🚨 What Causes KB5065426 Installation Failure?

The most common causes are:

• Corrupted Windows Update cache
• Broken system files
• Component store issues
• Conflicts with antivirus or network tools

👉 Most problems are fixable in minutes.

⚡ Quick Fix (Try This First)

Before advanced steps:

• Restart your PC
• Free up at least 10–20GB space
• Disconnect USB devices
• Disable antivirus temporarily

Then try Windows Update again.

🔧 Step-by-Step Fix (Follow in Order)

✅ Step 1: Run Windows Update Troubleshooter

Go to:

Settings → System → Troubleshoot → Other troubleshooters
Run Windows Update

👉 This fixes basic update errors automatically.

✅ Step 2: Repair System Files (SFC + DISM)

Open Command Prompt (Admin):

sfc /scannow
DISM /Online /Cleanup-Image /RestoreHealth

Restart your PC after running.

👉 This fixes most 0x800f0991 errors.

✅ Step 3: Reset Windows Update Cache

Run:

net stop wuauserv
net stop bits
net stop cryptsvc
net stop msiserver

Rename folders:

ren C:\Windows\SoftwareDistribution SoftwareDistribution.old
ren C:\Windows\System32\catroot2 catroot2.old

Restart services:

net start wuauserv
net start bits
net start cryptsvc
net start msiserver

👉 Then try installing again.

✅ Step 4: Install KB5065426 Manually

If update still fails:

1. Open Microsoft Update Catalog
2. Search KB5065426
3. Download correct version
4. Install .msu

👉 This bypasses Windows Update issues.

✅ Step 5: Still Not Working?

Try:

• Disable Fast Startup
• Perform Clean Boot
• Use System Restore

👉 If nothing works:

👉 In-place repair upgrade is the best fix

❗ Special Case: Network / Sharing Issues After Update

Some users report:

• File sharing not working
• Printer sharing broken
• RDP credential errors

Fix:

• Set network to Private
• Enable file & printer sharing
• Clear saved credentials
• Reconnect network devices

👉 These issues are usually configuration-related, not update failure.

💡 Why Error 0x800f0991 Happens

This error usually means:

👉 Windows cannot complete update servicing

Common reasons:

• Corrupted system files
• Missing update components
• Cache problems

👉 Not a hardware issue.

🛡️ How to Prevent This in the Future

• Keep enough free disk space
• Avoid interrupting updates
• Run SFC occasionally
• Keep backups

📌 Summary

If KB5065426 fails:

1. Run troubleshooter
2. Run SFC / DISM
3. Reset update cache
4. Install manually

👉 These fix most cases.

🔥 Final Tip

Windows Update errors look scary, but most are temporary.

👉 Follow the steps calmly — and avoid repeated forced installs.

Related guides (internal links)

・Why Does Windows Ask You to Restart After Changing Settings?

・How to Change the System Time and Date in Windows 11 (Beginner’s Guide with Pro Tips)

・Windows Won’t Boot After Update? Fix Black Screen & Startup Loops

タグ: Windows update, Windows, Windows 11, KB5065426, Error 0x800f0991, File sharing problems, Printer sharing