why string concatenation giving me error in this code? : <p>Basically I am writing a code to calculate CRC-16(modbus) value.</p>

<p>I have a frame which I pass to my crc calculator method.It works fine when I define my input string as a whole frame.But when I use two string and then concatenate them into one then i get error!I will put my code here to show what is giving me error.I can't understand why it is giving me error when I use string concatenation.I used one texbox and one button to display calculated CRC value.Please help.Thank you.</p>

<pre><code> using System;
 using System.ComponentModel;
 using System.Text;
 using System.Windows.Forms;
 using System.IO;

 namespace crccalculator1
{
public partial class Form1 : Form
{

    public Form1()

    {
        InitializeComponent();

    }

    private void Form1_Load(object sender, EventArgs e)
    {


    }
    private void button5_Click(object sender, EventArgs e)
    {
        String frameValue = 5000;//value to covert to hex


        int decimalNumber, quotient;
        int i = 1, j, temp = 0,p=0,y=0;
        char[] hexadecimalNumber = new char[100];
        char temp1;
        char[] chg = new char[100];
        decimalNumber = int.Parse(frameValue);
        quotient = decimalNumber;
        while (quotient != 0)
        {
            temp = quotient % 16;
            if (temp &lt; 10)
                temp = temp + 48;
            else
                temp = temp + 55;
            temp1 = Convert.ToChar(temp);
            chg[p] = temp1;
            p++;
            hexadecimalNumber[i++] = temp1;
            quotient = quotient / 16;
        }
        for (j = i - 1; j &gt; 0; j--)
        {
            chg[y] = hexadecimalNumber[j];
            y++;
        }

           string value = new string(chg);//here I get my hex value


        //string frame = "01060008"+value; // METHOD I TRIED ALSO DOES NOT WORK
       //string wholeframe = "010600081388" works!!
      //  string gg = string.Concat("01060008", value); // METHOD I TRIED ALSO WHICH IS NOT WORKING!
        StringBuilder builder = new StringBuilder();
        builder.Append("01060008");
        builder.Append(value);
        string x = builder.ToString(); //GIVES ME WHOLE FRAME

        var bytes = HexToBytes(x);
        string hex = Crc16.ComputeCrc(bytes).ToString("X4");
        textBox1.Text = hex;

    }
     static byte[] HexToBytes(string input)
    {
        byte[] result = new byte[input.Length / 2];
        for (int i = 0; i &lt; result.Length; i++)
        {
            result[i] = Convert.ToByte(input.Substring(2 * i, 2), 16);//HERE I AM GETTING ERROR !! as An unhandled exception of type 'System.FormatException' occurred in mscorlib.dll
        }
        return result;
    }

    public class Crc16
    {
        private static ushort[] CrcTable = {
    0X0000, 0XC0C1, 0XC181, 0X0140, 0XC301, 0X03C0, 0X0280, 0XC241,
    0XC601, 0X06C0, 0X0780, 0XC741, 0X0500, 0XC5C1, 0XC481, 0X0440,
    0XCC01, 0X0CC0, 0X0D80, 0XCD41, 0X0F00, 0XCFC1, 0XCE81, 0X0E40,
    0X0A00, 0XCAC1, 0XCB81, 0X0B40, 0XC901, 0X09C0, 0X0880, 0XC841,
    0XD801, 0X18C0, 0X1980, 0XD941, 0X1B00, 0XDBC1, 0XDA81, 0X1A40,
    0X1E00, 0XDEC1, 0XDF81, 0X1F40, 0XDD01, 0X1DC0, 0X1C80, 0XDC41,
    0X1400, 0XD4C1, 0XD581, 0X1540, 0XD701, 0X17C0, 0X1680, 0XD641,
    0XD201, 0X12C0, 0X1380, 0XD341, 0X1100, 0XD1C1, 0XD081, 0X1040,
    0XF001, 0X30C0, 0X3180, 0XF141, 0X3300, 0XF3C1, 0XF281, 0X3240,
    0X3600, 0XF6C1, 0XF781, 0X3740, 0XF501, 0X35C0, 0X3480, 0XF441,
    0X3C00, 0XFCC1, 0XFD81, 0X3D40, 0XFF01, 0X3FC0, 0X3E80, 0XFE41,
    0XFA01, 0X3AC0, 0X3B80, 0XFB41, 0X3900, 0XF9C1, 0XF881, 0X3840,
    0X2800, 0XE8C1, 0XE981, 0X2940, 0XEB01, 0X2BC0, 0X2A80, 0XEA41,
    0XEE01, 0X2EC0, 0X2F80, 0XEF41, 0X2D00, 0XEDC1, 0XEC81, 0X2C40,
    0XE401, 0X24C0, 0X2580, 0XE541, 0X2700, 0XE7C1, 0XE681, 0X2640,
    0X2200, 0XE2C1, 0XE381, 0X2340, 0XE101, 0X21C0, 0X2080, 0XE041,
    0XA001, 0X60C0, 0X6180, 0XA141, 0X6300, 0XA3C1, 0XA281, 0X6240,
    0X6600, 0XA6C1, 0XA781, 0X6740, 0XA501, 0X65C0, 0X6480, 0XA441,
    0X6C00, 0XACC1, 0XAD81, 0X6D40, 0XAF01, 0X6FC0, 0X6E80, 0XAE41,
    0XAA01, 0X6AC0, 0X6B80, 0XAB41, 0X6900, 0XA9C1, 0XA881, 0X6840,
    0X7800, 0XB8C1, 0XB981, 0X7940, 0XBB01, 0X7BC0, 0X7A80, 0XBA41,
    0XBE01, 0X7EC0, 0X7F80, 0XBF41, 0X7D00, 0XBDC1, 0XBC81, 0X7C40,
    0XB401, 0X74C0, 0X7580, 0XB541, 0X7700, 0XB7C1, 0XB681, 0X7640,
    0X7200, 0XB2C1, 0XB381, 0X7340, 0XB101, 0X71C0, 0X7080, 0XB041,
    0X5000, 0X90C1, 0X9181, 0X5140, 0X9301, 0X53C0, 0X5280, 0X9241,
    0X9601, 0X56C0, 0X5780, 0X9741, 0X5500, 0X95C1, 0X9481, 0X5440,
    0X9C01, 0X5CC0, 0X5D80, 0X9D41, 0X5F00, 0X9FC1, 0X9E81, 0X5E40,
    0X5A00, 0X9AC1, 0X9B81, 0X5B40, 0X9901, 0X59C0, 0X5880, 0X9841,
    0X8801, 0X48C0, 0X4980, 0X8941, 0X4B00, 0X8BC1, 0X8A81, 0X4A40,
    0X4E00, 0X8EC1, 0X8F81, 0X4F40, 0X8D01, 0X4DC0, 0X4C80, 0X8C41,
    0X4400, 0X84C1, 0X8581, 0X4540, 0X8701, 0X47C0, 0X4680, 0X8641,
    0X8201, 0X42C0, 0X4380, 0X8341, 0X4100, 0X81C1, 0X8081, 0X4040 };

        public static UInt16 ComputeCrc(byte[] data)
        {
            ushort crc = 0xFFFF;

            foreach (byte datum in data)
            {
                crc = (ushort)((crc &gt;&gt; 8) ^ CrcTable[(crc ^ datum) &amp; 0xFF]);
            }

            return crc;
        }
    }
</code></pre>
