‘send to’ ‘mail recipient’ does not open new mail message

We are running SBS2003 with workstations running XPPro, using Outlook 2003 as the email program. I have one computer that the ‘send to’ ‘mail recipient’ has stopped working. I have checked/tried all of the following:
1. Ensured that MS Outlook was the default both in Internet options and Add/Remove programs -Set program access and defaults. I have uninstalled the ‘Personal Folder Backup’ utility as per Microsoft Article 823672. I have run the Outlook Repair utility. I have unregistered and reregistered the sendmail.dll file. All to no results.

I do not want to uninstall and reinstall Outlook 2003. (Only as a last resort).

Any suggestions would be appreciated.