I agree with Zuluru: according to the code you typed, you are using the Auth component, and if you use the component, the correct code is normaly (at least in Cake 1.3):
$this->Auth->allow (‘index’);
But in order to be able to use this implementation, you need first to declare the component in the controller your are coding with the line:
var $components = array (‘Auth’);
The message returned by the server means that it doesn’t know anything yet about ‘Auth’. That is why it says “call to a member function ‘allow()’ on null”: $this->Auth returns null considering the actual implementation of the controller you are working on.