If when trying to uninstall the mailbox role in Exchange 2007 from a windows 2008 server you get the following error:
"An error occurred. The error code was 3221685466. The message was The service is already registered.."
Try changing the registry key value HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Exchange\v8.0\Mailbox\
from "Uninstall" to "Install". Make sure you use capital "I" as its case sensitive. Then try to uninstall the mailbox role again.
Tags: Exchange 2007, mailbox role, uninstall, error code 3221685466