Replying to icemanoich:
Still not working in 4.1.14.
Ubuntu 11.10 as a host and Ubuntu 10.10 as a guest. Work only if I safe state of VM (auto power off) and then I can take snapshot.
That's not true. It should be sufficient if you pause the VM (VBoxManage snapshot VM_NAME take SNAPSHOT_NAME --pause. If the VM is not paused then this is a live snapshot, which does not work, but taking a snapshot from a paused VM should work (and it works here).
We will eventually fix the live snapshot problem but currently there are other higher-priority items.