I use them together and I kept my Poser 4 installation to hand just in case but I work exclusively from Poser 5. It doesn't seem to be a compatibility issue with the actual Poser 5 file format, this appears to be the same as it imports all Poser 4 specific content without a problem. I would suggest mailing e-onsoftware about this, there may be something in the works to correct this. Best wishes Jody