Video Driver issues when editing in Mission Architect

Pretty much every time I edit in Mission Architect, my computer freezes. It'll happen either during creation of custom critters or when I test an arc and try to enter the mission at an AE building. The game crashes no other time - only when using Mission Architect - which is disappointing because it's one of the reasons I returned to City of Heroes last August.

Computer specs:

Phenom II X6
ATI 6850 1GB
8GB RAM

Anything else you need to know, just ask.