During as SBS2003 migration to SBS2011, while decommissioning the source server (SBS2003) before Exchange 2003 can be removed you will have to remove the routing group connector from Exchange 2003 and Exchange 2010. You can use the Exchange System Manager to remove the 2003 to 2010 connector. To remove the connector from the destination server 2010 to 2003 you will use the Exchange Management Shell using the below command.
Remove-RoutingGroupConnector -Identity “Exchange Administrative Group (FYDIBOHF23SPDLT)\Exchange Routing Group (DWBGZMFD01QNBJR)\DestinationServer to SourceServer” -DomainController DestinationServer.LocalDomain.local
Make sure you change the following first;
DestinationServer = name of new SBS 2011 Server
SourceServer = name of old SBS 2003 Server
LocalDomain.local = name of the local domain
The use of this code is done at your own risk.