Event 6 on RTM SBS2011

I'm getting the error below every half-hour on an RTM and clean intall SBS2011 server.  The server is fully patched including the Update Rollup 2 for Exchange 2010.

Cmdlet failed. Cmdlet Get-User, parameters {Identity=NT AUTHORITY\SYSTEM}

In the details:Microsoft.Exchange.Configuration.Tasks.ManagementObjectNotFoundException: The operation couldn't be performed because object 'NT AUTHORITY\SYSTEM' couldn't be found on 'SBS2011.contoso.local'

Pete