problem with retrieving data from access database (c# asp.net)

Input string was not in a correct format.

public void Search()
    {
        OleDbConnection conn = new OleDbConnection();
        conn.ConnectionString = "Provider=Microsoft.Jet.OleDb.4.0; Data Source=" + Server.MapPath("~/App_Data\\Database1.mdb");
        conn.Open();

        string sorgu = "Select * from Table1 where AD Like '" + TextBox1.Text +"'";

        OleDbDataAdapter adap = new OleDbDataAdapter(sorgu, conn);

        DataSet ds = new DataSet();

        adap.Fill(ds, "Table1");

        GridView1.DataSource = ds;
        GridView1.DataBind();

        conn.Close();
    }