Sounds strange. Some things that come to my mind:
Art thou  using no-script or ref-control? Is java script enabled in thy browser? Doest thou have permission to access the files thou want to upload (normally not an issue if thou use Windows)? Does photobucket or whoever perhaps filter some file extensions?
Thou could also try using a different browser if thou haven't already done that.
Or try another service, if it's a problem on their side, for example omploader.org (doesn't care what is uploaded, but might show offensive material in "recently uploaded").
 For some reason my spell checker doesn't like "you", so I resorted to thou for now .
 Since this is silly I'll try and fix it.