open your registry and find the entry for PoserSceneAsciiFile
Under this there is entry shell--Open--Command

Put the location of wherever you put executable plus argument of 1 (In my case it is "I:/PP2014/PoserPro.exe" "%1")

The actual key HKEY_CLASSES_ROOT/PoserSceneAsciiFile/Shel/lOpen/Commmand

But the associate file command should have taken care of this in first place, if for some reason the original install did not.