"Log on as a Service" permissions

I need to grant a user I created the "Log on as a Service" permissions. On my Windows 2K3SP2 Exchange 2K3SP2 server, I go to Local Security Settings-->Local Policies-->User Rights Assignment--> and double-click Log on as a service, the Add Users or Groups button is greyed out. Note all the blue icons options are not greyed out, but the only 3 grey icons items are all Greyed out....

I beileve this is a security issue as the button is greyed out...?

Please Help...

Tom...

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