How to redirect a not registered visitor to the register page

Hello,
I’m offering to the visitors to choose the theme and create the sub site in my multisite/budypress platform.
When visitor clicks on Essential Theme slide on the front page everything is working fine in case if user is already logged- in. If the visitor is not registered he has to be redirected to the registration form but instead I’m getting: “The page you were looking for was not found” I believe I messed up with Buddy Press. Please help. I was trying to solve it with Protected Content plugin had now luck.
If you need the access to my dashboard you are most welcome.
Thank you.