excerpt of my modules.conf
;
load => chan_modem.so
load => res_musiconhold.so
load => chan_zap.so
;
;
[global]
chan_modem.so=yes
chan_zap.so=yes


so when i start asterisk, the follwing shows up in my /var/log/asterisk/messages:
Aug 25 05:22:10 WARNING[1076939296]: /usr/lib/asterisk/modules/chan_zap.so: undefined symbol: ast_retrieve_call_to_death
Aug 25 05:22:10 WARNING[1076939296]: Loading module chan_zap.so failed!
Aug 25 05:42:26 WARNING[1076939296]: /usr/lib/asterisk/modules/chan_zap.so: undefined symbol: ast_retrieve_call_to_death
Aug 25 05:42:26 WARNING[1076939296]: Loading module chan_zap.so failed!

asterisk fails to start