Outlook E-Mail Problem

Once again, I turn to the readers of this site for help with a computer problem.

When I address a new e-mail in Outlook to someone already in my Contacts list, the message doesn't get sent. When I check the Outbox, there's the message, and in the delivery address (To:) box, the addressee's name and e-address now appear in single quote marks, which I didn't type. This was obviously generated by Outlook when I chose the recipient from my Contacts list, but it's causing the mail to hang and sit in the outbox. However, if I re-type the same message with the same addressee info manually, the message will be sent immediately. Since I use the Contacts list often, this is a pain.

Any idea what the problem is? Is there an option inside Outlook that I can toggle off to fix this? Anyone else run into this?