System.ArgumentException was unhandled by user code

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C#

SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["RegistrationConnectionString"].ConnectionString);
conn.Open();
string insertQuery = "Insert into Userdata (Username,Email,Password,Country) values (@Username,@Email,@Password,@Country)";
SqlCommand cmd = new SqlCommand(insertQuery, conn);
cmd.Parameters.AddWithValue("@Username", TextBoxUN.Text);
cmd.Parameters.AddWithValue("@Email", TextBoxEmail.Text);
cmd.Parameters.AddWithValue("@Password", Pass);
cmd.Parameters.AddWithValue("@Country", DropDownListCountry.SelectedItem);
Exception on this line System.ArgumentException was unhandled by user code
(No mapping exists from object type System.Web.UI.WebControls.TextBox to a known managed provider native type) cmd.ExecuteNonQuery();
Response.Redirect("Manager.aspx");
Response.Write("Registration is Successful");

conn.Close();