[Click] Problem with tap and TCP

[remi.clavier at orange-ftgroup.com]

 two PC (A & B) are connected via an ethernet cable eth0 <->eth0.

In each PC, the received frames on eth0 are transmitted to tap0 and the frame from tap are transmitted to tap 0

When I try to send a ping command from A after an exchange of ARP , the frame goes well from tap0 (A) to tap0 (B) an B answer a ICMP request.. The A console give good lines, sure thae the connection is correct

When I try to send a TCP command from A (telnet, ssh), the frame goes well from tap0 (A) to tap0 (B) but B never answer and A send a lot of time the same frame with SYN=0. Of course, the TCP connection between A and B can't be etablished.

PC are ubuntu based.
ARP table seems correctly filled.
Iptables is empty.

An idea to solve this issue and ready to help me interactivly ?
It's a very important problem for me.

Thanks a lot...