tried everything - all kinds of user names. Used Samba and AFP - all works fine on Jaguar - never works on Panther. Looks like an incompatibility of Panther with our version of Samba or Netatalk on the Server. Been in touch with Apple Support, with no result so far. I also found some hint in a Netatalk forum that there are some issues between Netatalk and Panther - similar to what I was experiencing. In the meantime, we also found out that if we are connecting through Classic on Panther, we may lose files that we save over the network! VERY insecure thing!