Found it!
In case you're wondering why this server was off the network from time to time, well, the poor thing was crashing. On a regular basis. Like a religion.
I made all the upgrades, I tried some tips from friends, but it kept crashing.
But now I know. Bad memory.
Well, I've removed the bad memory (at least I hope I did remove the right one...) so it should be more stable now.
BTW, memtest86 is available directly from any Fedora boot CD. Just type memtest86 at the prompt.
