Sam,
are you using the default map? Or have you loaded other contents to your map?
Clicking on the perl at the top left should not cause an immediate crash, it simply opens a menu.
Without knowing what you have in your map, do you have any other unexpected behavior prior to clicking the perl?
You could try for a reset: backup this directory : C:\Users\username\Documents\ArcGIS Explorer, then delete your nmf file/s.
When you start explorer, it will start in 2D with nothing other than the basemap. Then try clicking the perl. Let me know if you are still getting a crash.
Sam I would be interested to know what kind of layer is causing the issue when you start adding them back one at a time.
Thanks,
Edan