I got this message initially for the site wwf2.gooduse.co.nz when I didn't have the right database name.

Now I'm getting it in the backend admin when I try to edit a particular page type (ProjectPage). This clearly used to work because someone has added content on their local computer and i think it must have happened when I uploaded the site to the server... But I've re-uploaded it a lot and it's still there.

The error is really unhelpful and obviously means a whole bunch of different things...

Errors aren't displayed on live sites. Instead, they get emailed to the developer, for security reasons.

Add the following line to your _config.php

if(Director::isLive()) Debug::send_errors_to("developer@email.com");