Hi,
I have folder with Emails and this folder is reported as invalid offset of index. I can do "reindex folder" it does not report any error, but the problem is not solved anyway. The result is that there is not possible to delete any mail from such a folder. Reindexing will undelete them. I hope that his is a defect of Pegasus Mail itself. You can download whole folder just here. File bad_folder.zip contains it packed to shorten download time.
http://78.108.103.11/~fojtik/pmail/BAD_FOLDER/
I know the one workaroud this stupid situation. Create another folder, copy mails to the 2nd folder and then delete defective folder anyway.