Try to upload file with symbols such as "#" or "+" in file name via our standard SWF uploader. You'll see that when full url is built, it's incorrect because file name is not urlencoded. Also this is applicable to folder names in URL - for example, in URL http://www.sitename.com/system/part1/part2/filename.ext part1, part2 & filename.ext (& system?) need to be urlencoded. Another case is non-formatter URL building to uploaded files, I found one in OnViewFile event.