Traveler not resolving mail database

Traveler website shows the following prompt when a particular user logs-in : “The IBM Notes Traveler server cannot resolve your User ID CN=John Doe/O=Domain to a mail database”
User is in a secondary address book. Also tried an extended directory. Same problem.
All other users in the same secondary address books are working ok.

When I move the user to primary NAB it works immediately.

What could be wrong ?

Any ideas are highly appreciated.

Thanks
paul