I forgot to mention that the problem has nothing to do with the kernel being tainted (due to VMware server). I installed VMware server after being faced with the crashes, to give the Java user a "sandbox" which s/he could crash without taking down the real server. Only then I discovered that VMware server has a memory limitation to 3600MB (I guess because it's not a 64bit application).
I see exactly the same crash with a non-tainted kernel.
Kay