tcp/ip trouble

[Stan]

Hi,

I'm writing network device driver ( DM9000 ethernet controller ).
It works nearly all :-(

For example :
( SERVER is a program , MBX is my RTEMS box) 

MBX send --> SERVER 
MBX receive <-- SERVER 
MBX send --> SERVER 
MBX receive <-- SERVER 
etc.
This it working properly.

But :

MBX send --> SERVER 
MBX send --> SERVER 
MBX send --> SERVER 
etc.

After some datas to send, never datas are transmit and the message
'Still waiting for mbuf cluster.' appears.

It seems a succession of write over tcp/ip to fail.
While a succession of read/write working properly.

Obviously, these examples working properly if I use ppp over tty.

An idea ?
Thanks a lot.

-- 

- Stan