flexfax: I can't receive fax from certain fax machines

[shui@pointsnorth.com]

Hi All,

I get very frustrated to debug the problem with faxing from certain fax
machines.  I've installed hylafax4.0pl1 on Solaris 2.6.  Sending and
receiving is working.  However, faxing from some machines just won't work,
returning me a log like this:

Sep 23 14:27:53.68: [  614]: SESSION BEGIN 00000191 14032649466
Sep 23 14:27:53.75: [  614]: <-- [4:ATA\r]
Sep 23 14:28:01.95: [  614]: --> [4:+FCO]
Sep 23 14:28:01.95: [  614]: ANSWER: FAX CONNECTION
Sep 23 14:28:01.96: [  614]: RECV FAX: begin
Sep 23 14:28:36.40: [  614]: --> [7:+FHS:01]
Sep 23 14:28:36.40: [  614]: REMOTE HANGUP: Ring detect without successful
handshake (code 1)
Sep 23 14:28:36.40: [  614]: --> [2:OK]
Sep 23 14:28:36.40: [  614]: RECV FAX: Ring detect without successful
handshake
Sep 23 14:28:36.45: [  614]: RECV FAX: end
Sep 23 14:28:36.45: [  614]: SESSION END

and then hang up.  What might be the possible cause?  Is it the problem
with hylafax setup or on the fax machine?  I'm totally confused.  Could
someone please suggest what I can do?  By the way, my fax modem is
USRobotics Fax Modem 28800.

Thanks a lot for your help!

Sandie