I click on the Open Quiz Form button, and I'm asked to log in.

I click on the Open Quiz Form button, and I'm asked to log in. After a successful login I get a message: Wait until undirecting... After it nothing happens, the login window pops up again.

I did test Quiz Form app and did not find any issue with that. I was able to login to quiz form app successfully, select forms and set correct answers as well. Please check the screenshot below:

With which browser you are having this issue with? I would suggest you to please clear your browser cache and they try again. The following guide should help you how to clear browser cache: http://www.wikihow.com/Clear-Your-Browser's-Cache

Do try it out and get back to us if you have any trouble. 

I use Chrome. The problem was caused because of the cookies. I added the sight as an exception, but that was not enough. Problem solved since.

Thank you for your response.