http://support.microsoft.com/kb/2647882/en-us?sd=rss&spid=1167

This article contains steps to clean up the Active Directory when a Small Business Server 2011 Standard migration installation fails. If the setup of SBS 2011 Standard fails and the installation must be performed again, it is advisable to perform a system state restore on the source server and then retry the migration install. Sometimes it is not possible to perform a system state restore. This article contains the steps to clean up active directory so that a second attempt at installation will be successful.