One users mails not routed due to policy reasons on R5

We are running Domino R5 with Lotus notes clients. There is only one
server and one Internet domain used. Over 50 users can send and
receive emails to each other and to the Internet through the domino
server except one user. In fact he could send emails out a few days
ago but not today. He is a member of the Administrators people group.
He can send and receive emails within the domain and receive emails
from the Internet.

His Local preferences settings are identical to everyone else. But he
gets the error back in his mailbox, mail rejected, routing not allowed
through this server. The funny thing is, when I open his database on
the server using lotus notes as [Local] database and send emails out,
it works!

One suggestion online said go to the Lotus Adminstration,
Configuration, Messaging, Messaging Settings .... etc. But when I
click on Messaging Settings, a messagebox says "Server Error: Entry
not found in Index".

What database do I need to repair and how.