This may be a duplicate post..I've never posted a reply before.
I had this same error message with Windows Live Mail, but my outlook 2007
worked fine. AT&T and I found the following fix that is linked below.
See
thread #7... it instructs to delete a digital ID. When I did this it
worked.
All other previous attempts at different suggestions (liked listed by
others
here) did not work. See the following link:
http://www.vistax64.com/vista-mail/189028-windows-mail-error-0x800ccc0f.html