Posted a new doc on a bug in Max that can affect the SnapVertsToGrid modifier and any other scripted modifier: http://dev.wallworm.com/document/183/max_crashes_when_applying_a_modifier.html
The document discusses what causes this in your Max settings and how to fix it. Essentially, Max will crash if you assign any keyboard shortcut to use a BACKTICK key in the shortcut and later use a scripted modifier.