The default kickstart install dahdi-linux-2.6.1, and pbx_first_boot.sh try to install the old version of wanpipe :
/usr/bin/yum -q -y install wanpipe-3.5.25-kernel.2.6.18.274.3.1.el5.dahdi.2.6.0*
So an error occurred.
The script need :
/usr/bin/yum -q -y install wanpipe-3.5.26-kernel.2.6.18.274.3.1.el5.dahdi.2.6.1*