In general, it indicates that an page is not published yet. We will try to improve the error message.
Indeed, it means the page is not published yet. We are working hard to put the finishing touches on pages and then publishing them. The goal is to have every page available when 2.5.0 launches for real. At the time of writing this reply the domain model, forms, settings, security have been published.
Now after the release of 2.5.0 most is available, but I get the permission error for Module Security and Languages.
Is this a configuration bug or can anyone tell me when to expect full documentation?