On Windows 7 I was trying to run the FX SpringAnimation Sample app using "run in the mobile emulator" option.
I kept getting the " emulator 0 terminated while waiting for it to register!" message. So, I went over to my wife's Vista PC and was able to run the demo, but noticed that her McAffee popped up and asked for permission first.

So I thought perhaps it was Win7's Microsoft Security Essentials blocking something. I went into the advanced settings and saw that it only had one application excluded from the DEP (data execution prevention). Not knowing what exactly it was blocking that caused my problem, I toggled the DEP prevention to Windows apps only, rebooted and voila, problem solved.>