I just had my server up and running for about an hour.... now its giving me this error again and no one can join.... help??

----8/16/2010 3:10:33 PM ----
Type: SocketException
Source: System
Message: Only one usage of each socket address (protocol/network address/port) is normally permitted
Target: DoBind
Trace: at System.Net.Sockets.Socket.DoBind(EndPoint endPointSnapshot, SocketAddress socketAddress)
at System.Net.Sockets.Socket.Bind(EndPoint localEP)
at MCZall.Server.Setup()