Dial up Networking terminal service window

I am trying to dial into a client site with the "show terminal window" box
ticked because once this shows we have to enter a userid and password. 2 out
of 5 in the office cannot type anything into the terminal service pop up once
it comes up but the rest can. We have been through every setting in
properties and they are exactly the same from one that works to one that does
not. Is there anything else I can check?