Hi Mike,
Can you please let us know if you are trying to add more users to the project that you created before upgrading or is it a new project that was created after upgrading?
If its the old project, please go to Settings page and change the "Project Billing Account" to the one that was mentioned while subscribing. After this change please logout and login. It will work then.
If its a new project that was created after upgrading and you are still unable to add users, please provide details of the project to our support team (connect-support@trimble.com) - so that we can investigate this further.
Regards
Darshan