I made a 'bunnies' Custom Content Type.
I only added two fields. An image field, and a category (relationship to categories taxonomy) field. When trying to add an item, I get an Error: Item not found message..and the url shows an id=0, like
?page=pods_bunnies&action=edit&do=create&id=0
When I go back and edit the Content Type and add some arbitrary field that would actually save to the _pods_bunnies table (like a text field) instead of ONLY saving an id, I can successfully add an item and the url displays the new item id like
?page=pods_bunnies&action=edit&do=create&id=1