"Methinks the compression box should have disappeared at this point." Not disappeared but the compression option should have changed to either "Compressed" or "Uncompressed." Those are the only two available for the Photoshop format. Since yours did not change I can only guess that Poser still wanted to save it as a jpeg. I think that's happened to me before but can't remember why. I do remember Poser didn't lock up on me though; I just closed the warning and changed the settings and it worked.