Cannot accept/decline task request

OS:W2K
App: Exchange2K and Outlook 2000
Workstations: Win2K

I have a client that recently moved to a new office, no configurations were changed that any one can recall.

Prior to the move a specific user was able to create/accept/decline a task request for themselves and now they are given an error message:

“You do not have the permission to send the message on behalf of the specified user.”

This only affects this one user and all others are able to accomplish these tasks without error.

Any ideas?