Microsoft Knowledge Base Article 811272 contains the following summary:
When a node joins an existing server cluster,
the cluster
service performs a version check to make sure that the node that is joining has
a version of the operating system that is compatible with the
rest of the
cluster nodes.
The check makes sure that only validated and supported
configurations
run in a mixed-version environment during a
rolling upgrade.
The
checks are based on major operating system versions such as Windows NT4 and
Windows 2000.
The
rules that the cluster service implements do not cover
upgrades from
release candidate to
release candidate.
Microsoft
supports and validates
rolling upgrades from Windows Server 2003 RC1 or RC2 to
Windows Server 2003 RTM,
however,
you must first turn off the version check
feature.
For additional information about how to do this,
see the "More
Information" section of this article.
To
reduce the chance that a
rogue program compromises the cluster,
the default cluster security descriptor
that controls access to the cluster configuration and management APIs has been
changed from the Windows Server 2003 RC1 and RC2
releases.
If you upgrade the
operating system to Windows Server 2003 RTM,
you do not fix the security
descriptor automatically.
To make sure that the cluster is as secure as
possible,
manually fix the cluster security descriptor.
