Apple Mail: One Particular Junk Mail Message Will Not Move To Trash

Sorry if this has been answered earlier, but I can't seem to find a thread dealing with it. I have one particular message, marked as junk mail, which will not move to the Trash folder. Actually, there's one mail message, but the error message says that "three messages can't be moved to the folder Trash" associated with this account. Any ideas about how I can force delete this message? I'm using OS X 10.8.2 on a mac Book ProThanks. Marty

It's marked as junk, but is it in the junk folder? If so, what happens when you click "erase junk folder"? (I don't have 10.8, but in my mail it's <command-option-J>, I think)

Yes, it is in the Junk Mail folder. When I erase things in that folder, everything else deletes, except this message. I then get the same error message about three emails that can't be moved to the Trash folder.