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 Uncheck menu: View / Highlight Over Hovered Objects. This will eliminate the highlighting performed when the mouse hovers over an object which may reduce graphical/display requirements.
Note: If your system has "dual monitors", please try keeping FAB 3000 in the primary monitor.
Please let me know your results, and thanks again for evaluating FAB 3000.