If I am on the event page and not logged in a light red banner appears saying I need to login first before I can register for an event. When clicking on this banner i am rerouted to the 404 error page. Up to now I could not find a place where I can set the correct link to my login page.
you're right. You should insert there the right address to login into your site. If you are using Community Builder Login, it is an other address than the only normal joomla login.
if you don't find the right link to insert, you can use the line like that:
