Ok I changed it by upload, but it seems that the file must be Bitmap, and it is written on your site that it must be Jpg (dont know if it is a problem of translation...). Anyway, it doesnt work with Jpg and well with Bmp.
It really can be a jpeg, bmp or gif (no all gifs, i think so). I dont know why cant work with you jpeg, maybe a jpeg converted by a rare program or so... The only real limitation is that the file must be less than 500K