Interesting Security problem Can use some help

EmpoweredBizTech

Hello gang. I have the following issue at a clients location and I was wondering if any security guru's out there have any wisdom to share on it. The client is a Win 2k3 server, Exchange 2k3 and MS Outlook 03/07 environment. Users are receiving errors on some archived e-mails that they were previously able to open that states "Your Digital ID Name cannot be found by the underlying security system". I have reviewed the Knowledge base articles (831601 and 258527) along with some other research and I am having no luck. Nothing has changed and non of the certificates have expired. Any thoughts or feedback would be helpful. Thank you all in advance.