[lwip-users] Header Checksum error

[Roberto Romo]

Hi, 

right now I'm trying to implement the lwIP stack into the SMT32F4 to program a 
kind of TCP chat between a µc and a PC. 
With the Raw TCP.

I founded an example for a TCP-echo-client from st I think. When I compile it 
and run it on my µc everything is ok,
but when i capture the communication with  wireshark I see that the µc (IP: 
192.168.1.5) sends an error:

- Header checksum: 0x0000 [incorrect, should be 0x0d6f (maybe caused by "IP 
checksum offload"?)

Here is an image from the program:
http://blog.robertoromo.eu/wp-content/uploads/2012/02/checksum_error.png

I have to questions: 

1) is this error in the stack? or in the example I got?
2) does anybody knows I could I get it away?  

I have already read the "Design and Implementation of the lwIP TCP/IP Stack" 
from Adam Dunkels and the " Raw/TCP - WIKI " and really helped 
to build a small structure of what my project needs. Does anyone knows about 
more literature of implementations of the stack or an example for a "Chat" 
(With this I mean that, messages could be send at random times from client or 
server)

(Sorry about my English)

Regards
Robert