Property Size is not available for Database '[tempdb]

Hi

When i right click on my TempDB in Sql2008R2 i get this message:

TITLE: Microsoft SQL Server Management Studio
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Cannot show requested dialog.

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ADDITIONAL INFORMATION:

Cannot show requested dialog. (SqlMgmt)

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Property Size is not available for Database '[tempdb]'. This property may not exist for this object, or may not be retrievable due to insufficient access rights.  (Microsoft.SqlServer.Smo)

For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=10.50.1753.0+((KJ_RTM_QFE-CU).101210-2156+)&EvtSrc=Microsoft.SqlServer.Management.Smo.ExceptionTemplates.PropertyCannotBeRetrievedExceptionText&EvtID=Size&LinkId=20476

The link dosen't show anything. You are not allow running the EXEC sp_changedbowner ‘sa’ because it is on the TEMPDB.
I'm i going to restore tempdb? It works fine on all other databases incl. Master