bind on RHEL 4AS stops responding

We have RHEL 4AS running Bind 9.2.4-2 acting as our primary nameserver.
It is running all the latest Redhat Errata patches. Everything has
been running smoothly until a few days ago. Randomly this server stops
resolving IP's. There is nothing noted in the named logs or any other
log and the process is still running. This machine still has
networking and the load is not high. as soon as we restart the named
service all is well for awhile (sometimes hours sometime less). We
have tried disabling ipv6 on the server and rebooted, but the problem
persists. What would cause naed to suddenly become so buggy (again,
all configs on the box have been unchanged for awhile). Thanks in
advance!!

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