I have C7pro, with Windows XP and an Nvidea card. I have found that if I close a scene and C7 soon after, it takes a full minute to close properly. I usually get a windows error message in the process.
If I close a scene, wait 10 seconds, and then close C7, it closes in just 10 seconds more.
I assume that the memory handling routines for the file and the program interfere with each other when closing.