OE 5.5 won't load folders

A further problem with OE since I upgraded to IE/OE 5.5: Once or twice each day, if I try to switch from the Inbox to another folder, most commonly the "sent items" folder, it won't load the new folder. I can go to any of the other folders and they will load OK, but not that one. Sometimes, the same happens to a folder I've created under the "inbox" folder also. Shutting down OE and restarting doesn't help. The only way I've found to fix it is to restart the PC. When the "sent items" folder is refusing to load, OE won't send any emails - I just get an error message.

Alistair

 

The text of that error message would be helpful.