VM getting disconnected after changing preferred DNS IP

We have created a Virtual network(Cloud Only) and a Cloud Service,in that we have created two Virtual Machines.

First VM-Domain Controller

Second VM-Normal server

We have assigned Static IP for DC.We are trying to add Second VM to DC by assigning the static ip of first VM to preferred DNS ip of second server.But after changing Preferred DNS ip in the second server if we give ok.The RDP of VM getdisconnected automatically.

So help us to resolve this problem.

Thanks