Alright, I have a few things that I think might work.
First, just to clarify, make sure that you are uploading from iphoto library -- modified.
Secondly, MySpace has a limit on the maximum size of a photo file. When you modify, you may be exceeding that limit. Try Exporting and Re-Scaling the picture, then uploading. If not, it could be another myspace problem. =]
Good Luck.