RTC Connection Problem

Hi All, We had installed SQL Server and Navision Server in Two different Servers and Setup a delegetaion everything. We can connect to RTC from some of the clients Machine. Only Two Clients machine we face the problem of connectivity. In the Connection Window when we specify the Path of the Server we can see Companys list but when we click on the Company NAme to Open we are getting the following Error. "The Server "Net.tcp//svr2:7046/DynamicsNav/Service is either unavailable or connection has been lost. Only Two clients has this Problem. Please advise.