Help w/ "Outlook had problems encrypting this message"

[smackboy1]

I am using Outlook 2007 and Vista Business Edition (32). When someone whom I
have exchanged digital ID's with sends me an encrypted e-mail and I reply,
there is an error message "Microsoft Outlook had problems encrypting this
message ... recipients had missing or invalid certificates, or conflicting or
unsupported encryption capabilities". My choices are to send unencrypted or
to cancel. This is strange because I have their certificate saved under the
contact info. In order to send an encrypted reply I have save the reply as a
draft, then
restart Outlook, then send the draft and magically the encryption works. I
followed these suggestions http://support.microsoft.com/kb/555502 but it
didn't help. I've posted this problem before and tried removing and
reinstalling the sender's certificate. I used the Certificate Manager to
check the sender's certificate and trust authority (it's a COMODO digital ID)
and it all seems to be OK.

It's the most annoying problem because Outlook says there is a problem, but
as soon as I shut Outlook down and restart it, the problem goes away. It's a
huge waste of time because I have to restart Outlook everytime I want to
reply to someone.

 

[smackboy1]

I've been trying to different things. I've found that when I hit reply to a
encrypted message sent to me, Outlook doesn't seem to recognize the e-mail
address in the To: field as being in my Contacts (even if it is). It doesn't
"see" the digital cert from the Contacts. If I hit the To button and pick the
name from the Contacts list, then the encrypted reply works. If I manually
type in the e-mail address, it is not recognized as being in the Contacts.

However if the same person sends me a clear text e-mail and I hit reply,
Outlook recognizes the address in the To: field from the Contacts (it lists
the persons name and e-mail address).

Why is Outlook not making the link between the reply e-mail address and the
information in the Contacts?