I used Java 6 did *not* generate any RMI stubs, so I guess we can kill the stub rumor once and for all. I think the reason why I lost 3 points on network server was that I did not motivate why I used RMI well enough.
Probably the reason why I lost 12 on general considerations is, also here, that I did not motivate my design choices well enough. Mostly because I am not native in English (I'm Swedish) so I sometimes find it hard to be accurate enough in English.
Finally, I used the KISS (Keep It Simple, Stupid) principle. My GUI was very simple (obviously too simple) and I did not implement anything but what was required. In all, I have 18 classes (thereof 5 exceptions) and 59273 bytes of code.
Thanks all Javaranchers for the help, without you I would have failed. Now I will go for the SCJA certification, just for the sake of it.