Certificate error joining new Office Web App machine to farm

Hi ,
I have created Ofiice Web Apps Farm using Certificate . I am trying to join new machine to Office Web Apps fram however i get following error after running
PS C:\Users\owappdev> New-OfficeWebAppsMachine -MachineToJoin  existingfarmmachine
New-OfficeWebAppsMachine : Office Web Apps was unable to find the specified certificate.
At line:1 char:1
+ New-OfficeWebAppsMachine -MachineToJoin owadev2013.wpi.edu
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (:) [New-OfficeWebAppsMachine], ArgumentException
    + FullyQualifiedErrorId : CertificateNotFound,Microsoft.Office.Web.Apps.Administration.NewMachineCommand

I am running the above command on the machine that i want to join to the farm.  I have exported and imported the certificate to Certificate store on the new machine.

Any help is appreciated .
Thanks

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mp