Triggered by the last comment I did a bit more testing and searching the web and found finally the solution for the problem here: http://ubuntuforums.org/archive/index.php/t-79612.html
It was simply the missing package 'smbfs'. After installing it everything works fine and this bug can finally be closed. -- argument "credentials=..." doesn't work any more in fstab https://launchpad.net/bugs/48997 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
