asterisk users - Jun 2008 - busydetect=yes, busycount=5: hangup automtically without reason, why?

Hi All;

Why busydetect=yes caused this autmatic hangup happens
without any reson (while responding to entering the
digits in the IVR) I do not know! And what is the
solution I do not know.

I used busydetect=yes and busycount=5 in zapata.conf
to help me in hangup when detect the busy tone, but I
faced the following problem:

While I am calling to the Asterisk PBX, and during the
response for the IVR and enter the digits and the
code, it hangup by it self (whout any reason).

I do not if I have to increase the busycount for
higher values, or it is related to other paramters or
it is related to the
-DBUSYDETECT_COMPARE_TONE_AND_SILENCE option in the
Asterisk Makefile, even if it is related to that
option, really I do not know what shall I do and what
exactly things mean to be able to set something
resonable.

Any help?
Regards
Bilal