XP SP2 - have service requirements changed?

I have an app that installs two services. These are very simple and
just listen for connections on a port, do some stuff then go and do
the same thing again.

With XP SP2 RC2 (but not AFAIK RC1), if both these services are
enabled (either one on its own seems to be OK), on bootup the Service
Control Manager locks up just after intialising them - no services
that are setup later will start up, including networking, etc. until I
stop/restart one of my services.

This is code that's been working with only minor tweaks for 3-4 years
and is as far as I can tell in conformance with the MSDN documentation
for services.

As it isn't my code that's failing but Windows I have no hope of
working out what's wrong (tried a few things eg. setting a load order
group to make it load later). The MSDN differences page for SP2 makes
no references to changes to requirements for services that I can find.

Obviously the SCM locking up is an SP2 bug (it should fail my service
rather than falling over if something's wrong) but I'd like to work
out what I'm doing wrong if anything to cause it.

The source is in http://www.cvsnt.org/archive/cvsnt-2.0.49.tar.gz, in
the cvsservice and lockservice directories. There's an installable
version too...

Tony