with the old (2.x) SDK I used this to log someone with offline_access:
$session = array ( \'uid\' => $userdata[\'fb_uid\'], \'sig\' => $userdata[\'
With PHP SDK 2.0 (I guess), I just use it like
$data = $facebook->api( '/me', 'GET', array( 'access_token' => $userdata['fb_access_token'] ) );
This should work with the newer one to as it seems to be more of a clean approach than rather setting up sessions by ourself. Can you try?