I cannot delete certain e-mail from my Delete e-mail folder. I am running Vista with Microsoft Mail. The error message reads "Unknown Error" Thanks MisterJ

Try this again after rebooting your system.
If Micro$oft comes up with an "Unknown Error" then that's about all you can do.

At the following site, scroll down until you see "How to Remove a Stuck Undeletable Message in Windows Mail":

Windows Mail problems - Vista Forums

It's near the top of the page.

Hope this helps!