Can't figure out a strange issue. When I access to site.com/admin and enter access credentials, Magento redirects me to the login page again.
If I refresh the page or enter login credentials again, I will be redirected to dashboard.
After some inspection, I also noticed, that after the first login, cookie contain two different variables admihntml for site.com and .site.com.
I think it's the problem, but don't understand how to solve it.
This happened in Chrome only. FF and Opera are OK.