The logic here is this: you rename that file (you don't want to delete it, in case you're wrong about it) so Poser will create a new Prefs file with default everything, and Poser will open just fine.

You can sort (in Windows Explorer) to view your Poser folders and files by Date, newest modified files first. You'll see what changed and when, so let's say you had this happen two days ago, well. . . look a the file that was last modified on the 28th (today's the 30th)