After disabling/uninstalling Exchange from our source SBS2003 server, I'm getting these warnings:
Event 5020 "The topology doesn't contain a route to Exchange 2000 Server or Exchange Server 2003 sourceserver.domain.local in Routing Group [...]"
Event 5006 "Cannot find route to Mailbox Server CN=SOURCESERVER [...] for store CN=[...]", for Public folder, First storage group and Recovery storage group.
I followed the technet article here: http://technet.microsoft.com/en-us/library/bb288905.aspx (linked from the SBS 2003 - 2011 migration guide). When uninstalling Exchange, I got a warning about NNTP not being found in the registry, but that didn't seem relevant, and the uninstall continued. The server was subsequently removed from the domain and shut down, as per the instructions.
If I open the Public Folder Management console on the Exchange 2010 server, the public folders \NON_IPM_SUBTREE\EFORMS_REGISTRY and \Archived mails gives an error on "Update content". I haven't found anything else which indicates something is wrong. We never really used the public folders on the old server, so there isn't really anything lost. Can I just remove these folders and let them be created anew?