If you don’t want to wait or if your Xbox is in the other room, here is how you can close those hung connections from your Windows PC.
To allow remote admin connections, connect through FTP, download Q:\System\FileZilla Server.xml and edit on your PC to change the Admin IP Addresses to match your network IP address class (in my case, 10.0.0.* - default is 192.168.0.*), then upload back.
Install an older version of the FileZilla Server like. 0.8.9 from here - that is because the protocol has changed in later versions. You can uninstall the application and only keep the FileZilla Server Interface.exe if you want.
Run the FileZilla Server Interface and connect to your Xbox (default password is xbmpzilla, it can also be changed in the above XML configuration file).
On the right side you will see the active connections, right click one of them and use “Kick” to disconnect. Simples!
An added benefit from using the FileZilla Server Interface is that now you can change server settings without having to download and edit the XML configuration file every time ;-) not that you should need to, but but might be useful.