KerberosToken2 "InitializeSecurityContext call failed" "logon sess

I have added WS-Security (WSE2.0SP2) with KerberosToken2 to my client ->
Web service (W2K3) connection. Users, groups and service target principle
("service3/bts-vm.soapoc.local@xxxxxxxxxxxx" or
"host/bts-vm.soapoc.local@xxxxxxxxxxxx") are managed in a project specific
Active Directory domain.

However, I get the following error:
InitializeSecurityContext failed with the following error message:
A specified logon session does not exist. It may have already terminated

On our company domain the same code works fine, but the way! Furthermore the
WSE2 Kerberos2 sample from MS results in the same error in the project domain.

Any hints?

Markus Leder
.