problem opening attachments

[Guest]

One of my users just starting getting this message when she tries to
double-click an attachment to open it:

"The messaging interface has returned an unknown error. If the problem
persists, restart Outlook."

Restarting Outlook has no effect. It appears only to happen on attachments
from outside our domain. She is able to right-click the attachment, save it
wherever, say to the desktop. Double-clicking it on the desktop opens it just
fine. Any ideas? Thanks in advance.

 

[Guest]

Oh, also, Detect and repair is unavailable because user is a terminal server
client...