mdb2 prepare statement with multiple types

I'm using PHP 5.1.6 and MDB2 and trying to wrap my prepare/execute/fetchAll into a class so I can execute a select query with one line. The following code shows the Class that I've created and also doing the same query directly:

<?php
include_once "MDB2.php";

class db {

    private static $dsn = array(
        'phptype'  => "mysqli",
        'username' => "username",
        'password' => "pass",
        'hostspec' => "localhost",
        'database' => "dbname"
    );

    private static $instance = NULL;
    private static $statement = NULL;
    private static $resultset = NULL;

    private function __construct() {}
    private function __clone() {}

    public static function getInstance() {
        if (!self::$instance) {
            self::$instance =& MDB2::factory(self::$dsn);
        }
        return self::$instance;
    }

    public static function execQuery($sql, $types, $values) {
        if (self::$instance === NULL) {
            self::getInstance();
        }
        self::$statement = self::$instance->prepare(
                $sql, $types, MDB2_PREPARE_RESULT);
        self::$resultset = self::$statement->execute(array($values));  
        if (PEAR::isError(self::$resultset)) {
            // (this is where it fails)
            echo('Execute Failed: ' . self::$resultset->getMessage());
            return false;
        }
        return self::$resultset->fetchAll(MDB2_FETCHMODE_ASSOC);
    }
}

echo "<pre>";

$dsn = array(
    'phptype'  => "mysqli",
    'username' => "username",
    'password' => "pass",
    'hostspec' => "localhost",
    'database' => "dbname"
);

$sql = "select * from testtable where id = ? order by id LIMIT ?"
$t = array('text','integer');
$v = array('ABC',3);

// GOING DIRECT 
$db   =& MDB2::factory($dsn);
$stmt =  $db->prepare($sql, $t, MDB2_PREPARE_RESULT);
$res  =  $stmt->execute($v);  
$out  =  $res->fetchAll(MDB2_FETCHMODE_ASSOC);
print_r($out);

// GOING THROUGH CLASS
print_r( db::execQuery($sql, $t, $v) );

?>

The output of going direct works as expected, but the second attempt, going through the class fails with the PEAR error message "MDB2 Error: not found". I can't see what the difference is between these two approaches.

The Class works properly if I only pass a SQL statement with one ? replacement and don't use 'array()' to hold the types and values. If I change these, it works:

$sql = "select * from testtable where id = ? order by id"
$t = 'text';
$v = 'ABC';

I found the problem with my code. The line in the execQuery method that reads:

self::$resultset = self::$statement->execute(array($values));

should be:

self::$resultset = self::$statement->execute(      $values );

OOP is new to me so I was convinced the problem was with the class and method.

(I'm not sure if I should be answering my own question, or just put it in the comments)