Exchange 2010 – cannot create users after demoting DC

At one of our client sites, we had an issue where the client could no longer create exchange 2010 mailboxes after a DC was demoted.

After some poking, and trying the “set-ADServerSettings” commd-let, we found that simply deleting the mmc definition file from  c:users<username>appdataroamingmicrosoftmmcExchange Management Console “solved” the issue.