I was upgrading enigmail today, and after restarting Thunderbird, it gave me the message that “A previous install did not complete correctly. Finishing install”. I googled for a fix, then helped myself: Whenever the file C:\Program Files\Thunderbird\xpicleanup.dat exists, Thunderbird will give the message. I deleted it, and Thunderbird starts. Not sure if I broke something in the process, though. The newer enigmail version didn’t install, and any time I tried, it gave the error again. the final solution was to remove my chrome/ folder from c:\Documents and Settings\enno\Thunderbird, delete the xpicleanup.dat file, delete and reinstall Thunderbird, then reinstall all extensions. A hassle, but at least now I’ve got a clean and working mail client again.