Your banner uploads fine. I just tried the one from
http://som-squad.com/images_flash/banners/banner.jpg Try using IE. If you are already I don't know, I just uploaded it on my test account.
And sorry to say, but this site was coded for IE only.. 98% of our hits come from IE, and other browers require diff types of coding. I don't have time to code for 3 diff browsers, let alone know how..