Interesting. I'm not sure what would cause that. The the upload option works for me, and others. Someone submitted a map earlier today as well. Have you tried a different browser? Cleared your cache? I know Caelum changed some backend things to the site today so it may have borked a few things. I'll see if I can replicate the issue, but clearing the cache may fix it. As far as external links, we reupload to our Dropbox anyway, even with attached files, but thanks for letting us know.