Aku Ade Error Ni La.. Sape Leh Tlong?

[the cracker 0]

ni coding aku...

using System;

using System.Data;

using System.Data.SqlClient;

using System.Configuration;

using System.Collections;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Web.UI.HtmlControls;

public partial class createUser : System.Web.UI.Page

{

protected void Page_Load(object sender, EventArgs e)

{

}

protected void subButton_Click(object sender, EventArgs e)

{

String connectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;

SqlConnection connection = new SqlConnection(connectionString);

SqlCommand cmd = new SqlCommand(@"INSERT INTO loginData(UserId,staffName,staffDepartment,staffEmail)

VALUES(@UserId,@staffName,@staffDepartment,@staffEmail)", connection);

cmd.Parameters.Add("@UserId", SqlDbType.UniqueIdentifier).Value = usernameText.Text;

cmd.Parameters.Add("@staffName", SqlDbType.NVarChar, 50).Value = nameText.Text;

cmd.Parameters.Add("@staffDepartment", SqlDbType.NVarChar, 50).Value = deptText.Text;

cmd.Parameters.Add("@staffEmail", SqlDbType.NVarChar, 50).Value = emailText.Text;

connection.Open();

int i = cmd.ExecuteNonQuery();

connection.Close();

}

}

dpt error ni bile run..

System.InvalidCastException: Invalid cast from 'System.String' to 'Sy

[the cracker 0]

hehe da settle..