[Solved] ASP.Net ExecuteScalar Error: Specified cast is not valid

Getting error as Specified cast is not valid

I need to auto inremented id as IDN but Im getting errors in this code.

namespace WebApplication2
{
    public partial class WebForm3 : System.Web.UI.Page
    {        
        private void new_id()
        {
            string ConnString = (@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\koti\Documents\Database11.accdb");
            OleDbConnection conn = new OleDbConnection(ConnString);
                if (conn.State == ConnectionState.Closed)
            {
                conn.Open();
            }
            string str = "select max(IDN) from TableMINES";
            OleDbCommand cmd = new OleDbCommand(str, conn);
            cmd.CommandType = CommandType.Text;
            Int32 max = (Int32)cmd.ExecuteScalar();
            Label5.Text = (max + 1).ToString();
            conn.Close();
        }

Can you please help me?