Failing to connect Windows Small Business Server 2003 using RDC

i manage a small client/server network and used to be able to connect the Server using remote desktop connection from any host connected to the network. suddenly i started getting an erorr stating “connection has been disconnected by remote host”. i have tried the following:
-Reenable remote desktop support on the server.
-Scan for virus infection.
Both action did not help, the problem is still there.

Thanks
Dali