InvalidArgument=Value of '0' is not valid for 'index' error

private void comboBox3_SelectionChangeCommitted(object sender, EventArgs e)
        {
            DataSet3 _dataset = new DataSet3();

            OleDbCommand com1 = new OleDbCommand();
          

            com1.CommandText = "Select * from Dogovor where Komint=@Komint order by Brdog";
            com1.Parameters.AddWithValue("@Komint", comboBox3.SelectedItem);

            OleDbDataAdapter oleDBDataAdapter1 = new OleDbDataAdapter(new OleDbCommand(com1, conn));
            try
            {
               oleDBDataAdapter1.Fill(_dataset, "Komint");

//here you are making mistake before filling dataset you are trying to bind it to combo first fill the dataset and then bind it.

                comboBox2.DataSource = _dataset.Tables["Dogovor"];
                comboBox2.DisplayMember = "Brdog";
               

            }
            finally
            {
             
            }
            textBox1.Focus();
        }