How to fix three-times login?

I open BI-Server on the browser and type in my username and password. When I click "Login" BI-Server shows me a pop-up saying my login is invalid. Then I have to click login again (without changing anything), and the pop-up appears again. Then I click login the third time and it works...

How can I stop BI-Server to behave this way?

Thanks in advance!