获得函数声明的“语法错误,意外”,“”

I am getting

Parse error: syntax error, unexpected ',' in /xxx/login.php on line 28

the function is defined as :

function login($subuser, $subpass, $subremember, $fb = 0){
//something here
}

and I am calling it like :

$retval = $session->login($fbuserid, , , 1);  

I have been working on this for over 2 hours, and I just got this error, so I dont know how complex of an error it is as I just cant see anything wrong with the code!!!

Pass null if you want to skip a parameter. You can't just leave it blank. Only list support that, and that only because it's a construct and not a function.