Call_user_func expects parameter 1 to be valid callback, first array member is not a valid class name or object

See more:

PHP

forms

HTML5

website

Hello! I fixed my other problem, but, there is a problem i tried to fix for 2 hours straight. The error is: call_user_func() expects parameter 1 to be a valid callback, first array member is not a valid class name or object.
Here is a bit of my code:

public function bindQueryParams($stmt, $paramType, $paramArray = array())
{
    $paramValueReference[] = & $paramType;
    for ($i = 0; $i < count($paramArray); $i ++) {
        $paramValueReference[] = & $paramArray[$i];
    }
    call_user_func(array(
        $stmt,
        'bind_param'
    ), $paramValueReference);
}

If you need the full code, Please tell me. I also used a tutorial on how to make a sign up form so its NOT MY CODE.

What I have tried:

I tried it for two hours straight