...

This happens even if I change $Self->{FQDN} in Kernel/Config.pm to the new domain name. Any hints?

Yes, use the provided maintenance script:

/opt/otrs/bin/DeleteSessionIDs.pl --expire to delete expired Session IDs, or finally

/opt/otrs/bin/DeleteSessionIDs.pl --all to delete all IDs.

That was it! Thanks Sincerly, Klaus -- Klaus Steinberger Maier-Leibnitz Labor Phone: (+49 89)289 14287 Am Coulombwall 6, D-85748 Garching, Germany FAX: (+49 89)289 14280 EMail: Klaus.Steinberger@Physik.Uni-Muenchen.DE URL: http://www.physik.uni-muenchen.de/~k2/ In a world without Walls and Fences, who needs Windows and Gates