Freezing

I've gotten reports lately from my staff that some of there machines are "freezing" or "locking up" when they start NUDC, I have tried repairing the problem making sure the copies work, but as soon as they go online with NUDC 4.5.3 on 2 G3 iMacs and 1 PMG4 and the program starts and then stalls with a pinwheel spinning.

Im at a loss...