I tried the suggestion of moving out the *.cnm files. That didn't help, but I tried other files. When I removed cache.pm, pmail opened normally. The file doesn't look obviously corrupt.

Yesterday Pmail 4.52 started giving me a "Pegasus Mail for Windows has encountered a problem and needs to close" error immediately on startup.

Interestingly when the "Start in" folder was the PMAIL folder it seemed to start normally, but when it was another folder it wouldn't start. However it was not totally consistent. After some fiddling it started working normally.

 Today I'm getting the same crash, and it will not start from any folder. I tried re-installing, but no improvement.

 It's been a few days since the last Microsoft Update. There was a recent Adobe Reader update.

[quote user="jdudeck"]Yesterday Pmail 4.52 started giving me a "Pegasus Mail for Windows has encountered a problem and needs to close" error immediately on startup.[/quote]

This post links to a couple of possible issues. And here's another one. Doing a search on the forum might reveal even more ...