I've got a user who's getting this message when trying to send signed emails.  The certificates on her CAC were signed by CA-31, which is not included in Apple's SystemCACertificates keychain, so I downloaded and imported them into her login keychain, but the error persists.  There are no issues that I can see in Keychain Access… every related cert is valid.  She does NOT have the "certificate cancer" issue that was commonly associated with Entourage, unless it's manifesting itself in a way where the cert is correctly chained to DoD Root CA 2 but Outlook is trying to chain it to a fake/hidden/cached copy.  I'd asked previously about where Outlook caches certificates, as I've run into situations before where it clearly is not correctly reading certificates from the user's keychains, but nobody has ever been able to answer that.
I recently installed Mac OS X 10.9 (alias Mavericks) and noticed that encryption of outgoing emails is broken.
I can sign emails and I can decrypt emails I received- but the necessary certificates for encryption are not available. It seems the certificates of signed emails I receive are not added to the keychain and therefor not available for encryption. So far I have not found a way to manually add certificates to the keychain. Has anyone else noticed this problem? Is there a workaround or a fix to this issue?
I have really run out of ideas here.  All that I am trying to do is add certificates to contacts that I have in my address book.  When I go to the "Details" tab in an email and try to "Add Encryption Certificate to Contacts" it never shows up on the contact.  When I download the certificate manually then go to the contact hit the "+" button and try to add it, it seems like it is adding it but never shows up.

So far I have done a "rebuild" on the identity, created a new identity and tried every which way to add the certificates.  They just will not add...  If anyone could help me out with this issue I would very much appreciate it!