The sad thing about the IE8 - after installation, I couldn't find the way to get back to previous version IE))
Anyway, I had to make do with IE8 while debugging asp.net app and discovered that some times debug doesn't want to debug in IE))
After run debug - IE runs the window but after a few sec the debug is inactive.
The reason why it happens - the second instance of IE has been running already at the time you run debug. Just close ever instance IE before the run debug.