Reason 5 to 4? But from mac to pc...

Been making some tracks with a friend...he has Reason 4 (mac) and I have 5 (PC), and we were jamming some tracks out with MIDI controllers which meant that the tracks didn't really have any structure, and weren't mixed. He's given me the files on his laptop (including all the samples he's used and REX files) but I can't open his .rsn files for some reason (pun intended). The message "This file type is not supported" comes up...I know Reason 5 supports Reason 4 files because since I've upgraded I've been able to open old files created in Reason 4. Is it something to do with him using a mac and me using a PC?? Are the file types different?

From what I've read, .rsn files are supposed to be cross platform.

That's what I always thought...

Is his version of 4, fully updated?

Ah ok...strange. His files are saved as .rsn but they need to be .rns...just need to change the file extension. He must've done that himself...You'd think .rsn would just be short for Reason I suppose. All sorted :)