If you distribute files made with Pro Pack, non-Pro Pack users will experience the "newer version number than expected" error message, because Pro Pack has a higher version number than regular Poser. It's a simple fix: open the file with a text editor like Wordpad and change the version number from 4.2 to 4.01. The version number is usually near the beginning of the file. Likewise, you have to be careful with MAT pose files; some are intended for Poser, and others for Pro Pack.