Host lookup error in Navision 4.0

Hi, I have a very strange problem om a new Windows 2003 terminalserver. Whenever users start Navision 4.0 they receive “The TCP/IP connection host is not answering (tcp/ip econnrefused)”. But when i choose OK to the error Navision logs in as it should and everything works OK. The database is running on the same terminalserver and the client is connecting through tcp/ip, but this should not cause a problem ?? DNS is setup up correctly, i have checked host and service files and tried to enter the navision servername with ip adress of the server and local host ip adresse - but stille the same error. Hope any one can help