I have just migrated a company from a mixed 2003 & 2007 environment to 2010.
2003 server removed successfully without issue, however when trying to add the 2010 server as a public folder replica the issues began.
Lots of 1020 MSExchangeStoreDriver and 3091 Replication Errors in the event logs
Finally tracked the issue down to the server object in First Administrative Group in ADSIEDIT.
Open adsiedit and check if there any objects in
CN=Servers,CN=Fist administrative group,CN=Administrative Groups,CN=Erste Organisation,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=domain,DC=local. Is the container “CN=Servers”
If servers is empty, then delete it.