Today i ran into a very weird problem during the installation upgrade of an Exchange 2010 server. The server has all roles on one server ( CAS/HUB/MBX ) and cleany installed just one day ago, SP1 and Rollup 8.
After downloading SP2 and performing the setup i was suprised with an error screen:
Check your registry keys to see if one still contains Action = install
Go to the following HKLM\Software\Microsoft\Exchange Server\V14\
In my case i found the action key in \MailboxRole\
After exporting the affected key and deleting it, i restarted the setup/upgrade of SP2 and it executed as i was hoping for.