Installed SP3 yesterday. Sent .SLDPRT to CNC guy today. Can't open. Try to open a .SLDPRT that I sent two days ago. Opens fine. Sent a second different .SLDPRT from different computer recently installed SP3. Won't open. Only difference is SP3 from SP2. WTF?
I think that it can be caused by the file association. Please see http://www.thewindowsclub.com/change-file-associations-windows