asterisk -r
core set verbose 10
core set debug 10
exit

.. and you need to start fop2_server in debug mode:

service fop2 stop
cd /usr/local/fop2
script capture.log
./fop2_server -X 15

then do the call and transfer & transfer & transfer until the error happens.

Then stop fop2 and script:

ctrl-c
exit

You will have the manager log in the file capture.log . At the same time extract the last lines of the asterisk full log :

tail -n 5000 /var/log/asterisk/full/log >/tmp/asteriskfull.log

Those two files will have the relevant information to track the problem and determine if its a fop2 bug, an asterisk bug, a user error, etc... You would want to reduce verbosity and debug in asterisk when you are done and start fop2 as a service again:

asterisk -r
core set debug 0
core set verbose 3
service fop2 start

Best regards,