can't Login with GUI but works with Telnet

hello
i have changed something on the Network settings.
Then i had to reboot. After this the server was not visible in the network.
On the Console i changed again the settings to Eth0 , IP, Network, mask Gateway.
After this change i could reach the Server with telnet and Log in.
With the GUI (Webbroser) i could now also access and when entering the pwd i got a error:
Login failed. Please try again.
user name is root password ist copy pasted from a file so i am sure the password is correct.

what could be the reason any help or suggestion?

have a nice day
vincent