I have suddenly lost the ability to view any digitally signed messages in Outlook 2000. The preview pane just says 'Encrypted or encoded messages cannot be shown in the Preview pane', and opening the message brings up a dialog that says 'Can't open this item'. Checking my stored email, every signed message (the ones with the little red ribbon) does the same thing, even though they all worked fine two days ago! Any ideas what might be going on here?

Thanks in advance!