Fixed the problem!
(after hours reading the threads here and causing costs).
The problem is that Ralus HAS TO BE PAID FOR!!! Otherwise the communication between mediaserver and UNIX/Linux System won't be successful. The mediaserver can see the Linux-host but doesn't show any shares.
Why are there no hints at all, neither in the software (just a window appears, saying 'function not implemented') nor in the administrators guide?
Additionally, we do NOT want to pay once more for a piece of software, which is an essential part of BackupExec! We do not understand the VERITAS/Symantec customers policy here.
OK, everybody can take the workaround to install the FREE legacy 9.x/8.x client. This works fine!