PHP v5.4 and Class 'mysqli' not found error

Hello folks,

   I upgraded to Web Expressions 4 from Web Matrix 3. I also upgraded my PHP from v5.3 to v5.4.
I checked in the applications option to ensure it had the right path for the php and it does.
But when I try to execute my page this is what I receive:

Fatal error: Class 'mysqli' not found in C:\Users\laptop\Documents\My Web Sites\SuppliersPHP\agentlogon.php on line 18

So I looked it up and mysqli should still be valid.
The web pages worked fine under PHP v5.3 in Web Matrix 3.
But I need to have Web Expression 4 working properly as its time to retire Web Matrix 3.
Can someone tell me what is wrong and how to fix it?
I really need PHP 5.4 and Web Expressions to work properly.
I also found a snippet of coding that test to see if mysqli is installed and it returns that it is not!
How can that be when I successfully used with PHP v5.3 in Web Matrix 3?

I have also included the entire section

<?php 
    require_once ("Includes/dbconfig.php");
    include("Includes/session.php");
   
    $baderr= "";

    if (isset($_POST['cancel']))
        {
           header ("Location: goodbye.php");
        }

    if (isset($_POST['submit']))
       {
           $username = $_POST['username'];
           $password = $_POST['password'];

        // create database connection
        $databaseConnection = new mysqli(DB_HOST, DB_USER, DB_PASSWORD, DB_NAME);
        if ($databaseConnection->connect_error)
          {
            die("Database selection failed: " . $databaseConnection->connect_error);

          }else{

             $query = "SELECT * FROM agents WHERE AgentUserName = '$username' AND AgentPassword = '$password'";

             $result = $databaseConnection->query($query);

            if ($result->num_rows > 0)
               {
              // output data
                while($row = $result->fetch_assoc())
                   {
                      //set up global session vars to be used thru out pages
                        $_SESSION["UserType"] ="A";
                        $_SESSION["AgentRecId"] = $row["RecId"];
                        $_SESSION["MsSqlAgentId"] = $row["AgentIdPk"];
                        $_SESSION["AgentFirstName"] = $row["FirstName"];
                        $_SESSION["AgentLastName"] = $row["LastName"];
                        $_SESSION["AgencyName"] = $row["AgencyName"];
                        $_SESSION["AgentEmail"] = $row["EmailAddress"];
                   }
                     // close database connection and redirect to agents menu
                        mysqli_close($databaseConnection);
                        header ("Location: agentmenu.php");
           } else {
               $baderr = "Username/password combination is incorrect. Please try again";
           }
       }
    }
?>

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of coding below: