Most if not all of the Free Servers do not allow outside linking. If you are just trying to post a SWF file then it doesn’t matter. They allow that, you just can’t post GIFs JPGs BMPs or links to files. But if you have Brinkster or Angelfire or Tripod or any of those, they do allow posting of SWFs.
Change the image extension to something else such as txt and it will work then.