Hi,
I'm using VBox 3.2.10 under Slackware.
I tried to save guest machine state and I went out of space on harddrive. VBox informed me about it, but when I released some space on disk I was unable to save state machine again - the machine was grayed-out, disabled. I couldn't either save its state, or even force-power-off it. The window didn't respond in any way. I had to kill vbox processes.