OES 11 SP1 / SLES 11 SP2 - fully patched up to March 28th.

DNS service has a habit of dying. I was gone during the latest case,
but told my backup how to restart the service if it did die. How do I
figure out what is causing DNS to die? I checked
/var/opt/novell/log/named/named.run. The last entry before dying
05-Apr-2013 11:47:29.518 client: query: warning: client no more recursive clients: quota reached

The next entry (when my backup restarted the service) is:
05-Apr-2013 13:02:52.857 general: main: notice: starting BIND 9.3.2 -u

How to troubleshoot this?