Fix 0x800B0009 PERSIST_E_SIZEDEFINITE: Data Size Error

Quick Answer

Delete the contents of C:\Windows\SoftwareDistribution (stop Windows Update service first), then run sfc /scannow and DISM /Online /Cleanup-Image /RestoreHealth from an elevated Command Prompt.

What Actually Triggers This Error

I've seen 0x800B0009 pop up mostly during Windows Update failures, but also when someone's trying to install a certificate into the local machine store or running a backup tool that relies on volume shadow copy. The error code translates to "the size of the data could not be determined" — Windows is saying it can't read a registry value or a data blob that's supposed to have a fixed size. Usually this means some file in the SoftwareDistribution folder got corrupt, or a registry key under HKLM\Software\Microsoft\Windows\CurrentVersion\Component Based Servicing has lost its size metadata. I had a client two weeks ago who got this trying to install a security update on a Windows 10 Pro machine that had been running non-stop for eight months. A reboot fixed nothing. The root cause: a stuck pending file rename operation from a previous failed update.

Step-by-Step Fix

1. Stop the Windows Update service
   Open Command Prompt as Administrator and run:
   net stop wuauserv
2. Clear the SoftwareDistribution folder
   Delete everything inside C:\Windows\SoftwareDistribution. Don't delete the folder itself. Use:
   del /f /s /q C:\Windows\SoftwareDistribution\*.*
   If some files are locked, boot into Safe Mode first.
3. Restart the service
   net start wuauserv
4. Run System File Checker
   sfc /scannow
   Wait for it to finish. If it finds corrupted files, it will replace them from cache.
5. Run DISM
   DISM /Online /Cleanup-Image /RestoreHealth
   This fixes the component store itself. Takes 10-20 minutes.
6. Reboot and retry

If That Doesn't Work

Sometimes the corruption is deeper. Try these in order:

• Check registry permissions — Open Regedit, go to HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Component Based Servicing. Right-click, Permissions, make sure SYSTEM and Administrators have Full Control. If permissions are jacked, it can block size reads.
• Use the Windows Update Troubleshooter — Download from Microsoft's site, not the Settings app one. The standalone one is more thorough.
• Reset Windows Update components manually — There's an old script from Microsoft called "WindowsUpdateReset.cmd" that resets all the services, BITS, and cryptsvc. Run it as admin.
• Check certificate store — Run certlm.msc and look for any certificates showing a red X or 0x800B0009 in details. If found, delete and re-import the cert.

Prevention Tips

Three things I tell every client after fixing this:

1. Reboot at least once a week. Windows Update leaves temp files hanging around. A restart flushes them.
2. Keep your disk healthy. Run chkdsk /f every few months. Bad sectors can corrupt update data.
3. Never force-shutdown during an update. That's how you get orphaned registry entries that cause errors like this.