some users w2000 Prof. can’t telnet

I have two networks, they are connected with a router, in the first network I have one domain NT and users (w95 and w2000 professional) and in the second network I have severals Unix server. Yesterday I installed one Windows 2000 Advanced Server in the first network now some users Windows 2000 professional can not to do telnet to Unix server. When they try to telnet to Unix server they recive a message like this ” …. refuse … “. I don’t know what happen