java.lang.ClassNotFoundException: com/microsoft/sqlserver/jdbc/SQLServerDriver

I am really new to JAVA but need to call a SQL Server function which I have been given access to.

I have built a JAVA call into a pl/sql function and am successfully calling it from one of my environments. When I move to another environment I get the error

ORA-29532: Java call terminated by uncaught Java exception: java.lang.ClassNotFoundException: com/microsoft/sqlserver/jdbc/SQLServerDriver

I have researched this to death and checked the correct installation of JAVA which seems fine but I'm obviously missing something. I need to somehow trace what is different on this environment, the fact that it runs in the other envionmnet proves that the class is correct so it has to be a config issue.

JAVA Class

import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.net.Socket;
import java.io.IOException;

public class xxiceHJ
{
    protected static String JDBC_DRIVER = "com.microsoft.sqlserver.jdbc.SQLServerDriver";  
    protected static String DB_URL = "jdbc:sqlserver://999.999.99.99:1433";
    protected static String USER = "xxxx";
    protected static String PWD = "xxxxx123$";

    public static String getOrderStatus (String OrderNumber) throws SQLException, Exception
    {
        Connection conn = null;
        CallableStatement cs = null;
        ResultSet rs = null;
        String Message = null;
        String WarehouseId = "01";

        try
        { 
            // Register JDBC driver
            Class.forName(JDBC_DRIVER);

            //Open a connection
            conn = DriverManager.getConnection(DB_URL, USER, PWD);

            cs = conn.prepareCall("{call usp_get_order_status(?,?,?)}"); 
            cs.setString(1, WarehouseId);
            cs.setString(2, OrderNumber);
            cs.setString(3, Message);

            rs = cs.executeQuery();

            //if prodeure return a value
            if (rs.next())
            {
                Message = rs.getString(1);
            }

            //Clean-up environment
            rs.close();
            cs.close();
            conn.close();

//        }
//        catch (SQLException se)
//        {
//            //Handle errors for JDBC
//            cfFileNumber = "SQLException" + se.toString();
//            se.printStackTrace();
//        }
//        catch (Exception e)
//        {
//            //Handle errors for Class.forName
//            cfFileNumber = "Exception" + e.toString();
//            e.printStackTrace();
        }
        finally
        {
            //finally block used to close resources
            try
            {
                if (rs!=null)
                {
                    rs.close();
                }
            }
            catch (SQLException se2)
            {
                //nothing we can do
            }
            try
            {
                if (cs!=null)
                {
                    cs.close();
                }
            }
            catch (SQLException se2)
            {
                //nothing we can do
            }
            try
            {
                if (conn!=null)
                {
                    conn.close();
                }
            }
            catch (SQLException se)
            {
                se.printStackTrace();
            }

        }
        return Message;

    }



}