Following a successful contact merge job, Mailbox enabling fails.
In this scenario the user accounts that were failing to be mailbox enabled were part of a Enterprise Voice, Lync 2010 trial that was running at the same time as performing their migration. The Lync 2010 installation was preventing the Disable-MailUser command from executing, this command is the first of a series of commands that NME uses when Mailbox enabling a user.
Once the user account was removed from the Lync 2010 trial it was possible to run the disable-mailuser command.
It was also found that the account in use in NME to provide rights to Exchange had the AD attribute "AdminCount" set to 1 from previously being a member of domain admins which prevented security inheritance from cascading the required rights to the account.
This Microsoft forum thread was useful in resolving this environmental issue:
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