There are a couple of reasons why this message is displayed:-
1) You are not assigned to an organization that has access to OpenGround - Your Internal Bentley Administrator will be able to check that your Bentley Login has been assigned to their account. If not they will be able to add it or submit a support ticket to have your account assigned to the organization.
2) Your organization is using Named user licenses and you have not been assigned a license - Information on how to assign licenses can be found on this page https://virtuosity.bentley.com/how-to-get-started/.
If you are unsure who your administrator is then this article will help https://communities.bentley.com/communities/other_communities/licensing_cloud_and_web_services/w/wiki/52644