[Serusers] SER & PSTN

Hi All I installed a SER and configured it to send the calls to a PSTN gateway. then i configured a cisco gateway for sending the calls to SER.in tis scenario there is no any problem and all the things work fine. after that i replaced the cisco gateway (that originated the calls) with a windows messenger 5.0 and started the test again, but it failed with error : "You cannot have a voice conversation with 18008782897(a)panaisp.com. This person needs one or more of the following: a computer sound card, version 4.0 or later of Windows Messenger, permission from his or her network administrator." I read the debugs and saw error : "Media Type(s) Unavailable" I replaced the windows messenger with SJPHONE but this error repeated agin "session rejected: 488 Not Acceptable media" I don't know the meaning of this error. Any experience? Alireza