Can't clear or delete flagged email from to-do list

I have a few old items in my to-do list (old flagged emails) that won't
delete and won't clear. Emails are no longer in the folders they used to be
on. Possibly deleted.

The error message is
"the folder "xxxx" cannot be selected. this may be because of a limitation
of your imap server or the folder may have been deleted or moved"

How can I removed these "ghost" items?

i'm using outlook 2007

-Tania