When you log in to the Dynamics GP web client site, do you get a security certificate error? You need to use the fully-qualified domain name for the machine in every place that it's needed, such as when you supply the URL to access the web client.
That means you should be using hr-fin-v.ad.technomuses.ca/GP
to access the web client. That should also be the full name that you saw when you chose the security certificate for the Session service.
If the names aren't consistent, you'll see security certificate errors, and the login won't be successful.