Please use Streams insted of this

NetMessage.buffer[num].writeBuffer[num3] = (byte)prefix2.Length;
for (int i = 0; i < prefix2.Length; i++)
{
    num3 += i;
    NetMessage.buffer[num].writeBuffer[num3] = (byte)(prefix2[i] & 255); // string is utf-16 (unicode)
    NetMessage.buffer[num].writeBuffer[++num3] = (byte)(prefix2[i] << 4);
}