demian my friend (and fellow fvwm user!)
the MB can indeed eat memory, it is wierd that it starts suddenly like this though, i ma guessing it has been working good for well over a year. i would check for something which may cause shorts, but this is unlikey. certainly compileing the kernel would not cause this, but perhaps a BIOS setting be screwed up. I know the sig11 is indicative of a bad memory location, so you may wish to try out a app called tufftest which checks this stuff out, when i had it you get a free copy for personal use.