I have uploaded an image of the Warning I get when I save an existing Custom Post Type. I can't seem to find what is causing the problem. However, it may be linked to a second problem I'm having and that is in using 'Display Template' for one of the CPT's. It just returns a '404' page all the time. I tested it all out on a duplicate site and used the Module Manager to export/import to this new site.
Can any help with what I've done wrong. Thanks