I too (and others) had the same problem, and found the solution you mentioned after trial and error. See the link <http://community.pmail.com/forums/thread/20732.aspx>

The Pegasus Mail IMAP function needs to be simplified, as many E-mail services are using IMAP now.

I set up a Gmail imap connection to my existing Gmail account. Pegasus populated the screen with similar "folders" that show in my Firefox connection to Gmail -- including the individual messages.

But now, a day later, I cannot open Gmail. There is only a mailbox labeled Gmail at the my mailbox level. There is no "+" to the left of it. When I click on it a little flag goes up and down. None of the folders of the account display.

How can I correct this?
Windows XP. Pegasus 4.63

Never mind.

I found in another thread

http://community.pmail.com/forums/thread/31251.aspx

that I had to right click the Gmail icon and close it, then reconnecting in [Tools] [IMAP profiles]