I have a laptop (1440 x 900) and an external monitor (1920 x 1200), and I'm running Virtual PC 2007. Initially, my VPC could not switch to fullscreen mode on my external monitor because the max resolution for VPC was only 1600 x 1200. I installed a hotfix ( http://support.microsoft.com/kb/958162 ) and after the hotfix, I was able to view VPC in fullscreen mode on my external monitor, but now I'm unable to view fullscreen on my laptop. It says "please check that the resolution of the guest is not higher than that of the host". I even tried to decrease the resolution of my Virtual PC to less than than of my laptop, but it always resets it back up.
So now after the hotfix, I can view fullscreen mode only when my external monitor is plugged in.
Any way I can resolve this?