when sending fax getting disconnected from RDP session.

Question

I have US Robatics usb fax modem on windows 2008 R2 server . the moment i wanna send the fax or even call out to my cell phone from windows  my RDP connection is dropping , on event viewer i am getting  termdd event id 56 .

looks like receiving fax is working fine but when i hit sending i am getting dissconnected from RDP connection.

Plase advise .

Thank you.