Outlook 2003

Hi
I have a user who keeps getting the following error in Outlook 2003 when she tries to assign people tasks. “Object could not be found” From there, the recipient never receives the message, and to her it shows that the message is awaiting a response from the user. I tried detect and repair, i even uninstalled and reinstalled the application. The temporary solution that seems to work is if I create a new user profile. However, the key word is tempoarary, about a week or 2 after the new profile is created the same error resurfaces.

The OS is XP Pro, and we have some other business applications running on the machine. Has anyone come across this problem and is there one clear way to fix it.
Thanks,