Import 2 different gerber file set to compare -> Click on tool -> Compare Layers -> Select the layers to compare -> Once it is done comparing see any of the results -> These results will be shown in a “zoomed In” type view -> Now move your mouse to the error on screen and software will crash for windows 7 64 bit.
If possible please save the workspace file (*.wrk) and I'll be happy to review it in detail. Without any other information and since you mentioned it involved the mouse movement, please go to menu: Setup / Options..., select tab "View", and uncheck the option "Display Mouse Object Hover". This will eliminate the highlighting performed when the mouse hovers over an object.
Please let me know your results, and thanks again for evaluating FAB 3000.