i have problem conecting Cisco 2quintum

Hi

When i connect ssw and send calls from my sipura or my sip dialer to quintum it does work , without any problem
but when i try to connect a Cisco 3600 using my ssw as a RTP Proxy
the calls fails and i have the fellowing error message on my sip log on the quintum :

sipsyn xxx syn:RequestMessage:: decoding headers failed

any idea about that

my ssw is voipswitch