I recently changed to 2012 SP2 from 2011. I am finding that sometimes when I import a STEP file (from a vendor web site) when I go to save the resulting .sldprt I get a "unknown error has occurred" error. It does not matter where I try to save it. The workaround I found was to export the .sldprt file to a step, import that step and then I am fine. Anybody else run into this? It may be specific to this one vendor but the file does import to a valid solid.
I can't up load the STEP file but here is the vendor page: