mountain lion not compatible with this computer
I'm trying to upgrade to Mountain Lion from Lion and the App Store won't let me because of the error message "Mountain Lion is not compatible with this computer". Why is this happening? Can I get around it? OR am I doomed to buy a new computer. This computer is around 5 years old and I would really love to not have to buy a new one.
Thanks
Mac Pro, Mac OS X (10.7.5)