More high CPU utilization with TFTP.NLM

We are experiencing intermittent high CPU utilization by TFTP.NLM,
similar to that described by Rick Pummel in this newsgroup this past
September. When it occurs the whole server slows, preventing our
nightly backups from finishing in the available time window. When the
problem occurs TFTP.NLM will not unload, and the only workaround we've
found is to reboot the server. Our situation is not as persistent as
Mr. Pummel's, though. It may be days or weeks before the problem
occurs, so using a packet sniffer to try to find errant TFTP packets
could be difficult.

We are running NetWare 6.5 SP6 (with miscellaneous patches to fix all
the things that the SP broke) and ZfD 7 SP1 IR1. The imaging server is
a DHCP server as well. TFTP.NLM is version 2.05.02, dated January 9,
2007. We do not have an Arecont video surveillance system like Mr. Pummell.

Ideally I would like to fix this problem, but if it requires a call to
Novell support I don't know that I want to go to the trouble and expense
since we don't use PXE boot for imaging very often. If no one knows of
a fix or at least a troubleshooting method, is there a way to
temporarily or permanently turn off preboot services at the server in
such a way that it won't unreasonably slow down our hundreds of
computers that will keep trying to boot to LAN?