Heinz.Wrobel at freescale.com reports:
if the GPGol Add-In from gpg4win 2.0.0, 2.0.1rc1 is active in Outlook
2003 SP3, the the LiveMeeting 2007 "Meet Now" function will no longer
open an invitation email template with the right information, but an
empty Rich Text email identical to what would happen for "Ctrl-N".

Disabling the Outlook Add-In reverts to proper behavior, i.e., when you
click "Meet Now" in Outlook, you get an invitiation email template with
all the necessary information in the email body and a preset Subject
line.

http://lists.wald.intevation.org/pipermail/gpg4win-devel/2009-September/000873.html
and:
What you have to have to reproduce the issue is an installed LiveMeeting
2007 client, the Outlook Add-In for 2003, and that on the machine of
someone with a login to the service.
Without the login, you can't use "Meet Now", i.e., you wouldn't see the
problem of the broken invitation mails.
http://lists.wald.intevation.org/pipermail/gpg4win-devel/2009-September/000877.html