Can’t log in Magento Admin

Look for the file:

/app/code/core/Mage/Core/Model/Session/Abstract/Varien.php

Arroud the line 100:
call_user_func_array('session_set_cookie_params', $cookieParams);

Add bars to comment the line:
//call_user_func_array('session_set_cookie_params', $cookieParams);

Done!

Now you will be able to login.