asterisk users - Feb 2005 - incoming call high failure rate on pickup of call.

Hi,
I have a sipura 2000 ATA connected to an asterisk server on the local
network, and the POTS line connected to asterisk using a X100P clone, when
calling remotely through the X100P (incoming call), the phone attached to
the sipura device always rings like it should, however sometimes it does
not pick up the call, when it does not pick up the call the telephone
attached to the sipura 2000 is completely silent, and the remote phone
making the call you still hear the ring like if the call was never
answered. When it does pick up the call it works fine.

I really do not know if this is an asterisk problem, a X100P problem, or a
sipura 2000 problem, The sipura has the lastest firmware 2.13g, asterisk
is running 1.05, and the X100P is usind zaptel drivers 1.04.

Any pointers or hints to what could be causing this problem ?

I am located in Mexico Tijuana.

I have been trying to solve this problem for several days without any
success.

Any help will be greatly apreciated.

Thanks,

Sergio