Send and Receive Fax with Dialogic

Dear all,
The Fax function is working fine in my Asterisk (ver. 1.2.7) and spandsp 0.0.2 pre 26 with normal fax machine. But if the destination site is using Dialogic VFX as a Fax machine, my Asterisk box cannot receive or send fax with the remote machine. Anybody have a experience about this coz I have no any ideas. I suspect there is a incompatible fax tone between Dialogic and SpanDSP but I m not sure.

Thanks a lot.