Actually, those are requirements for forums and photo albums (for uncropped pics). For cropped pics, the requirement is: a pic should be as small as possible. Cropping takes a lot of system resources and memory, it cannot process big pics. I cannot tell you what exactly is "big", it all depends on how busy is the server at the moment. Just keep resizing it until it goes through, or even better: upload a small pic as avatar. It will be resized to 190 x 190 px anyway, so not much point in uploading something huge, keep it small.