We shipped a FreePBX-based server with OpenVox DE130E card about 6 months ago and our client reported yesterday that all DAHDi PRI trunks are offline and reboot server won't solve this issue. FreePBX web admin panel shows Asterisk cannot load DAHDi module. When invoke module load chan_dahdi.so in Asterisk console it returns ERROR complaining cannot find channels or whatever. After hours of googling it seems that DAHDi Configuration module in FreePBX will deliberately overwrite customized configurations in /etc/dahdi/system.conf file every time someone access that module's settings page and eventually cause PRI card cannot be configured correctly.
It is easy to solve this issue - disable DAHDi Configuration module and re-configure /etc/dahdi/system.conf file. This should keep FreePBX from touching that configuration file. Another way would be leave the module enabled while put customized configuration in /etc/dahdi/system_custom.conf file (it doesn't work with me, probably need a newer version of the module).