That's because you're probably using the free package right? It only allows for 1 download at a time to happen, and chances are, you're probably sharing your IP address in some way (yes this is possible, I've read it on numerous places) with another machine which is also downloading files at the moment. Either way, Rapidshare sux, the free package has way too many limitations and I haven't been able to download their files even once due to the "The requested file does not exist" error. Long live uTorrent!