deleting emails

I am unable to delete emails from outlook 2000..
I can move the files to another folder, I can print them and I can send them... but I cannot delete them...

when I try to delete them I get the following message
"the messaging interface has returned an unknown error. If this problem persists, restart outlook."
I am using word as my editor, but it doesn't matter if I use HTML or plain text I have the same problem
Dennis