That was a good hint, Ron, I did some researching on this one. But the configuration of the machine is a bit different from a standard Ubuntu install, and so after a while I got impatient and decided to reinstall. Maybe I was fiddling around too much on the command line or it was not such a good idea to run the web gui on several PCs simultaneously, or.... Well, the problem didn't reappear on the new install so far, I hope it won't. If it doesn't for a while, I'll close this thread. Thanks, anyway.