"Invalid certificate" error after installing new digital ID

[David Rowell]

Got new digital ID from Verisign for my business e-mail account, downloaded,
installed, etc., then enabled "sign messages" function in Outlook 2007;
everything looks correct, "settings" tab inside "e-mail security" shows the
digital ID, the e-mail address in the digital ID properties matches the
Outlook e-mail account I'm sending from, and so on. Even so, when "sign"
button is selected in new message I get "cannot sign or encrypt because no
certificate matches this e-mail account."

What am I doing wrong?

Thanks in advance . . .

David Rowell