I downloaded and installed these virtual machines for IE8/IE9 web development, IE9 stays running but it appears the IE8 VM is constantly shutting itself down, and it is saving the state (it doesn't boot fresh) so I think it is Vbox. How can I debug what is causing this specific VM to shutdown. It is stable when I use it and only happens when I am not watching it, it never happens when I am using the VM.
heavyd is right.
In the Windows guest, open the command prompt and enter
(not --rearm as cited in that post, since this is Windows). You can do that up to twice apparently, to extend by 30 days each time. Apparently the iectrl tool from ievms also works but I didn't try that.