Exchange 2010 - new user creation / legacy mailbox problem

I inadvertently forgot NOT to create an Exchange 2010 mailbox for a new user, and instead used the ADUC (which homes to a 2003 server). Now I have a Legacy Mailbox for this new user. I have tried:

Set-Mailbox "username" -ApplyMandatoryProperties

But it returns the following error:

Can't apply mandatory properties on mailbox "username" because it is hosted on a legacy exchange server (not true of course).
*CategoryInfo : NotSpecified: (:) [Set-Mailbox], TaskInvalidOperationException
*FullyQualifiedErrorId: 2336176B, Microsoft,Exchange,Management,RecipientTasks.SetMailbox

Google is leading me in a circle and I need to get this fixed. Any reply appreciated.
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use ADUC to view the user's attributes properties. Looking for msExchRecipientType for this user and compare with other. By default normal mailbox user will have this attribute as 1

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Simon Butler (Sembee)ConsultantCommented:
If you have Exchange 2003, then move the user to the Exchange 2003 server, then move them back. If you don't have an Exchange 2003 server, but you still have the Exchange 2003 tools installed - remove them. If you manage a legacy user with Exchange 2010 tools, or a 2010 mailbox with 2003 tools you will usually break it.

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