NT Telnet probs conecting outside proxy

Hi!
I am having problems after reinstalling NT4 with sp6a connecting to an outside telnet sever.
The internet connection is through MS Proxy and since the reinstallation telnet doesnt seem to connect at all. It worked fine before the reinstallation. And Workstations that did not have the reinstallation done still can connect.

Any ideas anyone???
I have a niggleing feeling that it could be a sid issue

Paul