Exchange 2007 SP1 has been released (and there are dozens of reviews, tips etc).
Now, I know Exchange 2007 is a huge, complex product ... but every single SCC cluster I've built has had the same issue updating to SP1.
The official Microsoft documentation is pretty clear. You move everything to one node, update the other with setup /m:upgrade, stop the CMS, move it to the updated node, and upgrade the CMS with setup /upgradecms. What could be easier?
Except that every single time I've done this, virtual or physical, single or multiple nodes; every damn time I get the same failure to upgrade the CMS.
Setup previously failed while performing the action "Install". You cannot resume setup by performing the action "BuildToBuildUpgrade".
Wait ... the mailbox installation worked just fine! No errors at all. No warnings. But your clustered Exchange server is offline and there's nothing in the release notes or the MS doco to tell you what's wrong.
There are several pieces of guidance that suggest removing the Action and Watermark values from the registry works; it sure did for me. Check for values in:
HKLM \ SOFTWARE \ Microsoft \ Exchange \ v8.0 \ *Role
I had values in "ClusteredMailboxRole" but I've seen plenty of reports that values can also be present in the MailboxRole key. I also had to run setup /upgradecms twice, because in my case Exchange failed to flush the logs to disk even though I used the Exchange Command Shell to stop the CMS. Nasty (nearly lost a database).