Cross Domain Login doesn't seem to be working properly

Domain Mapping is working properly in my site. Main site is, and subdirectory mapped site is

The problem is when I login to, and then visit, I'm not logged. If I want to comment on a post, for example, I have to log in again in the mapped domain.

I have the "Cross-domain autologin" set to YES.

Any ideas on how I can solve this?