Microsoft Knowledge Base Article 811272 contains the following summary:
When a node joins an existing server 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
The check makes sure that only validated and supported
run in a mixed-version environment during a
checks are based on major operating system versions such as Windows NT4 and
rules that the cluster service implements do not cover
release candidate to
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.