Problem sending emails

Hello,

When sending emails, I receive the following error messeges intermittently:

"Some errors occured while processing the requested tasks. Please review the list of errors below for more details"

When I click the "Error" tag, it only shows an empty box without any error!!!

In fact, the mail was sent successfully (my recipient acknowledged receipt) but it remained in the "Outbox" folder and kept sending automatically. I have an option to delete it away from the "Outbox" folder to stop it from being sent again and again, but deletion will mean that I will not have a copy of the mail sent in my "Sent Items" folder.

Any one has any idea what is wrong with my mail box. I am using Outlook Express 6 for my emails.