I have heard of others with the same problem. Any compiled software with Visa refnums were crashing in LV 6.0. Perhaps you can upgrade to 6.0.2? I am not sure if this will work, though. Also, LV 6.1 is coming out soon, and it might be fixed.
Call NI tech support @ 1-800-IEEE-488 (ironic in this case, isn't it)
-Jim