The following code changes the hexadecimal string to a byte array by parsing the string byte-by-byte.
public static byte[] HexStringToByteArray(String hexString) { return Enumerable.Range(0, hexString.Length) .Where(x => x % 2 == 0) .Select(x => Convert.ToByte(hexString.Substring(x, 2), 16)) .ToArray(); }