Error "Workspace could not be started. environment ____ not valid or authorized"

A customer was added as a collaborator to a project but encountered an error during attempts to start a workspace:

Experimentation showed that choosing a different Compute Environment got beyond the above error but they needed to use the specific Environment that had been defined for the project due to certain library requirements.

Resolution:

The default Compute Environment set for the project was not globally accessible, rather it's visibility was restricted to a specific Organization.  To solve the problem the user needed to contact other members of the Organization which owned that Organization and have them add him to the Organization.