Navision 2015 webclient login problem

Hello,
I have little problem with sign into webclient. I set up windows authentification on web.config file in C:\inetpub\wwwroot directory.
When I log into client from http://localhost:8080/xxxx/WebClient/ from server , i can log in without problem. But if I use real server name instead localhost, server will ask me for password. When I fill in it and click on OK, web client display me security windows again.

Thanks in advice
Best Regards