I maintain a fairly large database in our Outlook Program.
Everytime i try to delete one of our contacts from the Contacts folder, I
inevitably receive the following Error Message:

"The Messaging Interface has returned an unknown error.
If the problems persists, restart Outlook."

This is a serious bug and I can't seem to get around it. No matter what I
try.

fyi - to try to address this simple but serious issue, I have:

-- Restarted Outlook - and tried to delete again, as I was told to do.
-- Downloaded & installed all available updates for Outlook and tried again...
-- Tried to delete individual Contacts in various ways:
1) by trying to delete when the individual Address Card window is open
2) by trying to delete an individual contact when the entire contacts
list is open in the View by "Address Card" format
3) by trying to delete an individual contact when the entire contacts
list is open in the View "by Category" format
4) by trying to delete the entire "DELETE" category that I created
specifically for all of these 'to be deleted contacts' in the hopes that
someday I will actually be able to delete the suckers. They are numerous and
counting...

I always get this same error message when I try to delete any contact in the
contacts folder - no matter how I try.

you should know that this error occurs regardless of what method of deletion
that I try: It happens whether I:
1) use the "delete key" on my keyboard
2) use the "X" (delete) tool on the file menu aof the overall Outlook
Program Window
3) use the "X" (delete) tool at the top of the individual "Address
Card" Window.

How can i get rid of these contacts/names that are adding unnecessary bulk
to my database?

Why is Outlook refusing me the right to maintain my own database as I see fit?

With many thanks for your advice...