1. There is NO download manager that can be "lightning fast" for a downoad with a single connection that is usual for file/video hosting services. It may be only more comfortable in file management in this case.
2. Rapidshare is heavy loaded after some other file hosting services have been closed or have limited their activity. It seems that RS also uses more strict limitations for its users now.
3. You haven't named your FDM version so I can't help you with network management in FDM.
Andrzej P. Wozniak, FDM user and forum moderator
Read "How to report a bug or a problem with FDM"