Empty Login-Window

I have a Linux-Server in my office(Kubuntu 8.04, Kernel 2.6.19) with Open-SSH. Firewall is open on Port 22. I cannot login to the server, for I do get an empty Login-In Window. I think, the problem ist not the server. I have tried to login from my PC at home. There, I do not have problems.

Which window do you have empty? The login dialog or the authentication window?

It was the Authentication window.
But meanwhile I found the mistake. It was a wrong line im my Linux IP-Tables firewall.

Sorry