Can’t delete messages from out box in office outlook 2000

I have 4 messages in my out box that I am unable to delete. When I highlight them and press delete I receive the following message “The messaging interface has returned an unknown error, if the problem persists restart outlook”.

I am unable to use outlook anymore as it continues to send these 4 messages but does not delete them. Any help would be appreciated. Virus checker is up to-date.

Cheers