When installing Exchange 2007 SP1 in Cluster Continuous Replication (CCR) configuration. The setup of the passive node fails with the following error:
"This is not a passive node. A clustered mailbox server represented by the cluster resource group [clustername] was found on this node."
I've found out that the reason for the problem is that upon finishing the Exchange Cluster installation on the active node the setup will ask you for a restart. Restarting the machine will cause the Windows cluster to failover to the passive node to be and thus causing the Exchange installation to fail on that node.
To solve this problem make sure to move back the cluster resources to the active node and re-run the Exchange 2007 SP1 installation on passive node.
This solution was tested on Microsoft Windows 2008 and Microsoft Exchange 2007 SP1