Tcp client misses data

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VB

Hello,

I have a TCP-Server installed on my Arduino Mega2560, and an TCP-Client on windows in visualbasic.net 2015.
When i send a short code to the server it is received fine.
A short response code from the server to the client works fine also, however, when the response is bigger I receive only parts of it (very incomplete). It looks like a buffer overflow or so.

Thank in advanced.
JJ

What I have tried:

I have tried to find a solution on the internet, but till now I wasn't successful.
This is my vb.net code:

Private Function TCPConnect(TCPMessage As [String]) As String
If (TCPMessage.Length > 0) Then
Dim ServerIP As String = "192.168.0.10)
Dim ServerPort As Int32 = 10000
Dim Client As New TcpClient(ServerIP, ServerPort) 'Create a TcpClient.
Dim data As [Byte]() = System.Text.Encoding.ASCII.GetBytes(TCPMessage) ' Translate the passed message into ASCII and store it as a Byte array.
Dim stream As NetworkStream = Client.GetStream() ' Get a client stream for reading and writing. (Stream stream = client.GetStream())
stream.Write(data, 0, data.Length) ' Send the message to the connected TcpServer.
data = New [Byte](256) {} ' Receive the TcpServer.response. Buffer to store the response bytes.
Dim responseData As [String] = [String].Empty ' String to store the response ASCII representation.
Dim bytes As Int32 = stream.Read(data, 0, data.Length) ' Read the first batch of the TcpServer response bytes.
responseData = System.Text.Encoding.ASCII.GetString(data, 0, bytes)
TCPConnect = responseData ' Return variable with response from TCP-server.
stream.Close() ' Close stream.
Client.Close() ' Close client.
Else
'TCPConnect = "Error: Empty String" ' Return variable wit response from TCP-server.
TCPConnect = "Empty String"
End If
End Function