Korg Poly800/EX800 Users

I try a demo version of MQ8, it works very well with my others synths
(Roland D), but I can't get no communication from the Korg poly800II 
to the computer, only a flashing "waiting" or a negative message 
depending on the MQ8 driver I use (sysex missing something...). I am 
sure that the harware works properly because with my Cakewalk5, the 
dump request is followed by a good transfert. Is there any timing 
parameter to adjust ?
Thanks for help.

Stephen