I have the same problem.
What I do for now is running the PovRay file by clicking on the "run" button in PovRay and then it works, but it would be nice to find out what's going on.
I've tried to change the output directory, I've uninstalled povray and then installed it back, but it didn't help.
See previous post :
http://www.ac3d.org/forum/viewtopic.php?t=1721