Symptoms

Error "There should only be a single RMS Shared Identity user" appears when Exchange upgrade process is going.

Cause

There exists a duplicate account FederatedEmail.<ID> in Exchange.

Resolution

Remove the double FederatedEmail.<ID> e-mail account by using the adsiedit tool as described on Microsoft Answers:

To do this, follow these steps:

  1. Click Start
  2. Click Run
  3. Type adsiedit.msc
  4. Then click OK.
  5. Locate the Default Naming Context node
  6. Then locate to the CN=Users container.
  7. Locate and then right-click the CN=FederatedEmail.<ID> container.
  8. Then, click Delete.
  9. Re-run upgrade

In case this you cannot choose account to delete or if you remove one and that did not help - remove all those two federatedemail account and then create a new one.

  1. Remove both accounts
  2. Rerun the Exchange Server 2010 Mailbox role setup application.
  3. Create a new federated e-mail account by using the following command:

    PS> New-Mailbox -Arbitration -Name FederatedEmail.<ID> -UserPrincipalName FederatedEmail.<ID>@<Default_Accepted_Domain>
    

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