Exchange 2007 BuildToBuildUpgrade error

Whilst recently installing the Hub Transport role of Exchange 2007 SP1, the installation failed because it could not start the OpsMan server (it was disabled, another story). After enabling the service I went to reinstall the role and had the error shown below, indicated that I needed to perform the “BuildToBuildUpgrade” action.

After checking out the Exchange Team Blog (http://msexchangeteam.com/archive/2007/05/21/439529.aspx) it looked like I needed to remove a registry key.

Delete Watermark

Delete the Watermark key and restart your Exchange installation. For me, the Hub Transport role had successfully installed, it just looked like the installation said it had failed after unsuccessfully trying to start the OpsMgr services as one of the last tasks in the installation.