Hi,
I have been having problems with upgrading Adobe Reader 8.1.2 because an MSI file it was looking for had been deleted. On trying to update to 8.1.3, it would trundle along and then complain that the previous MSI file couldn't be found. (Why vendors insist on putting uninstall files in the Temp directory is beyond me...)
After trying various ways to fix the problem, the only fix I found that works is to use the MS Windows Installer CleanUp Utility. It threw an error, but did the job successfully.
http://support.microsoft.com/kb/290301
I don't yet know if this will also solve the problem of undelete-able Flash executable files.
Cheers,
Scott.