I had a similar problem with a thumbnail image which the form validation error said was in excess of the 200 x 200 pixels. I have my thumbnail application set to a maximum of 200 x 200 and when I checked the size it was only 180 x 200 (and under 15kb) so I uploaded the same image again and it went up fine. I've noticed quite a few changes on the site recently so I'm guessing the system is perhaps a little 'testy' for now.