Fangthane

I think that's your problem. I've seen quite a few people come forth with the very same complaint. It seems that many mobile devices just don't play well with the uploading feature of the site. Possibly some limitation in how they handle java scripts.

addendum:
The only workaround that I'm aware of, is to simply upload the picture that you want to show up as your ad's thumbnail, then use Photobucket's IMG tags to embed the rest of the pictures.