Alice No Longer Opening on Mac (Leopard); XCode conflict?

I was running Alice 2.0.7 for OSX 10.4 with no problems under 10.5.4 on an Intel MacBookPro. Then a little later on the same day, I installed the latest XCode developer tools from Apple in order to work on some other programming tutorials that I am considering for my students. When I went back to Alice and tried to start it up, the icon would bounce a couple of times in the Dock and then stop. I then tried deleting the copy and reinstalling it from the disk image, downloading a completely new disk image, installing the 2.2 beta, and uninstalling my XCode tools completely and rebooting. Nothing is working. I don't get any error messages.

I've downloaded the PC version to Parallels and that seems to be loading OK but I really do want to know what is going on with my Mac version since that is what I am teaching with.