omg! vista and windows mail problem

got a new cert, it installed fine with vista and IE7.

for testing, i use windows mail (the old outlook express) and an AOL account (the aol address matches the address in the certificate).

i then send a SIGNED email (using my new cert) to a different address.

when the message arrives (via outlook 2007) the subject line says “there are problems with the signature, click the signature button for details”

clicking the button brings up a window that says “digital signature: invalid”

the details button then says the message has been altered.

what i am TRYING to do here is to sign a message and send it to another address so that the other address can then use the cert to send an encrypted message back to myself to test functionality.

what is going on here and why is this so complicated???