It was something in poseidon.pfefs - don't know what exactly (this behaviour I've never seen before).

I was a bit sensitized to poseidon.prefs, because in the past (some MOS releases ago) I'd some troubles with poseidon.prefs too. Suddenly MOS did'nt want to boot! It stops after loading kernel. I found out, that poseidon.prefs causes that. Booted from another media and deleting poseiden.prefs always helps in this situations. In later releases this occours only rarely, if at all.