This usually happens when the user you are trying to use does not have a role in the workspace, that would allow access to the GoodData portal, but only viewing of embedded dashboards.
This can also happen if you are logged in with a user who does have this access, but then in the same browser you use for example some SSO tool integrated with GoodData to log you in as user who is embedded viewer only - in that case your new (more restrictive) session can override your original session.