Outlook Error: "Could not complete...."

[SharenF]

I had the error "Could not complete the operation. One or more parameter values are not valid." when trying to send emails from outlook.
The fix was that I had to delete the email that was in the outbox.
This email seemed to have no to recipient.
I was using Outlook in an office that uses MS Exchange Server.

I was using Outlook from Office XP and MS windows small business server 2000.

I am using Outlook from Office 2010 with Windows 7 Pro. There is nothing in my outbox, so I am still stuck. The email I am trying to send is one to be forwarded and I wonder if that's the problem. Maybe I should copy the offending email and then try to send it?