I encountered error 51E while installing an update to Windows Live Photo Gallery through Vista's update. Unfortunately there was no download from Microsoft to install this offline. This was the first time I had encountered this error code on windows update. Searching the web revealed others had encountered 51E but during installation of Vista SP1.
The solution
- Disable Carbonite
- Disable Avast on-access scanner.
- Use windows update to install the update - successfully!
- Re-enable Avast and Carbonite.
Just disabling Carbonite (as suggested by some for the Vista SP1 error) did not work, neither did just disabling Avast.
Hoping this helps someone else with the same problem.