When reading data, you need to determine how much data was really taken from the stream (buffer will not always be full).
The
clientSocket.ReceiveBufferSize
does not tell you how much data was buffered, it only tells how much memory is used for buffering.
Try something like this:
int count = networkStream.Read(bytesFrom, 0, (int)clientSocket.ReceiveBufferSize);
dataFromClient = Encoding.ASCII.GetString(bytesFrom, 0, count);