mac has a feature called "security context" which causes the node to fail resolving domains after a while.
see e.g: http://osdir.com/ml/unix-porting/2010-05/msg00000.html

symptoms:
 - works as long the console which invoked the script is up
 - works until process goes in background

possible workarounds:
 - invoke as: /usr/libexec/StartupItemContext ./script.sh
 - run as root
 - run with launchd

(i tried the first option... lets see if it works)