Forum Can not login from forum page.
 

There was a different thread about this before, but the solution did not work for me.

Every time a user tries to log in from the main forum site, then a page loads up, but then goes straight back to the log-in page. However, when opening other parts, it says you are logged in.

I've changed the url to .domain.com as it should be, but it doesn't work. Changed cookie path to /forum/ as there is my forum located, but doesn't work either.

The point is that I've bought a main site, and within a second domain name.

1. main site I use for personal gain.
2. redirection for a new site, with own domain name.

The 2nd one is a forwarder with the same FTP access as the 1st one, does that make a difference?

How to fix this?