Yeah, that problem is a bitch. Had the same thing and
wrote a post on it. I'll copy it into here...
I've solved the problem. I mean to use this post to share
the solution to others who have had this problem. It
happens when you import email into outlook and reply to
one such email. If you do not have the person that you are
replying to listed in your contacts, this error can occur.
The solution is simple:
1. Open your outbox
2. Double click the first email that is unsent
3. Change the email address from the alias such as 'Joe
Error' to the actual address that looks something like
(e-mail address removed).
4. Repeat for all the emails in this folder.
5. Relax! It is fixed.
