Password -not required!

I have built a space with many pages connected to it. In fact, they are 5 pages all with links on the homepage.
You don't need username/password to go from page to page.
However. my problem is that one of the five pages requests a username and password. How can I deactivate this login?? Have checked the code and can't see anything.

If anyone knows how to fix this, please let me know. Thanks.