are you sure its the right file type? you can post photos that get really big, I think up to 10,000pixels, I've posted pictures that were around 9000 X 7000 pixels, so I'm sure you should be able to, also, make sure that the file is fully uploaded when your posting, It should let you
yeh this is the first time that this has happened. Ive tried various file types starting with Tiff the biggest but for some reason they keep compressing them. not sure if a premium account would change things. Even Facebook has changed the way it looks and I uploaded a PNG to that one.