index was outside the bounds of the array. c#

public void ProductCode()
        {
            ulong urunkodu = 200000000000;
            int i;
            int counter = 0;
            int productcodefilecounter =0;
            string line;
            ulong barkodnumarasi;

            try
            {
                System.IO.StreamReader file =   new System.IO.StreamReader("malincinsi.txt");

                while ((line = file.ReadLine()) != null)
                {
                    counter++;
                }
            }

            catch (Exception ex)
            {
                MessageBox.Show("Malın Cinsi File could not be accessed. " + ex.Message);
            }
                 
            string[] ListLines = new string[counter];

            counter++;

            try
            {
                System.IO.StreamReader productcodefile = new System.IO.StreamReader("productcode.txt");

                while ((line = productcodefile.ReadLine()) != null)
                {
                    productcodefilecounter++;
                }
            }

            catch (Exception ex)
            {
                MessageBox.Show("Product Code File could not be accessed. " + ex.Message);
            }

            string[] ListProductCodeFileLines = new string[productcodefilecounter];

            try
            {
                for (i = 0; i < counter; i++)
                {
                    if (comboBox1.Text == ListLines[i])
                    {
                        urunkodu = Convert.ToUInt32(ListProductCodeFileLines[i]);
                    }
                }
            }

            catch (Exception ex)
            {
                MessageBox.Show("For iteration was unable to enter " + ex.Message);
                //Here ex.Message says Index was outside the bounds of the array.
            }

            double g = Convert.ToDouble(textBox5.Text);
            g = g * 1000;
            ulong ig = Convert.ToUInt32(g);
            barkodnumarasi = urunkodu + ig;
            textBox6.Text = Convert.ToString(barkodnumarasi);
        }