I'm having a similar problem with Poser myself as of recently. Sometimes when I load a non-conforming hair prop and either try to change lights (by using the Delete Lights) script or trying to render it (having Raytracing on), it acts like it's busy and just waits. If I click on it too many times I get the "(not responding)."  However, the problem is not with V4 for me.

Are you using Poser 7?

-R.