If you don't quote everything that has been suggested so far, you're
likely to get the same advice over and over from those of us who
can't easily go back to previous messages in the thread.
Download and install this hotfix, with Windows Mail not running:
http://support.microsoft.com/default.aspx/kb/941090
Although it's labelled as for mail stuck in the Outbox, it also works in
other folders suck as Deleted Items. If you don't know whether you
have a 32-bit version of Vista or a 64-bit version, try the hotfix for
the 32-bit version first, but if that refuses to install, also try the
hotfix
for the 64-bit version. If both refuse to install, try the Vista SP1
update as well if you haven't installed it already. Certain common
antivirus programs, such as most of those from Norton or McAfee,
tend to cause stuck messages and other problems in Windows
Mail, so if you have such a program, keep this reply in case you
need to try fixing the same problem again. A recent version of the
Trend antivirus program also causes assorted problems in Windows
Mail.
http://support.microsoft.com/kb/936330