Your script is timing out. I would recommend porting the codes to be run via telnet...I wrote a Mod awhile back that I no longer link in my web site, but it is available in the DBMAN Customization Forum in an older Thread. This Mod can be run via telnet/Cron. The only problem is that you can not easily customize the message that is sent.
If you do not want to port the codes to run via telnet, I would recommend asking your hosting company to increase your CPU timeout rate to above 60 seconds, actually couple minutes would be ideal.
Of course, you could also upgrade to DBMAN SQL, which runs more efficiently and faster than flat file database programs like the standard DBMAN.
Regards,
Eliot Lee