Exchange 2010 SP3 RU1 set-distributiongroup -managedby @{Add='Bill Broom'} problem

[PS] C:\Windows\system32>Set-DistributionGroup "Exchange Project Team" -ManagedBy @{Add="Bill Broom"}
All groups must have at least one owner who manages membership, message approval, and other settings for the group. Mak
e sure you assign an owner for this group.
    + CategoryInfo          : NotSpecified: (:) [], RecipientTaskException
    + FullyQualifiedErrorId : A2CF7793

I know this group has an Owner it has 2 infact but this happens on the Server and local Exchange Powershell.

You can over ride the settings using the:- Set-DistributionGroup "Exchange Project Team" -ManagedBy "<domain>\<userid>"

and that works. but I would rather not do that because of the legitimate owners of the groups.

Has anyone come accross this before?

Thanks in advance