Pages in this category have an ID on them that is improperly formed. (All IDs must be eight characters long and start with either "00" or "xx".) There are numerous templates that show IDs. {{ID}}, {{IDs}}, and {{IDs2}} display IDs directly, while others, like {{Creature Summary}} and {{NPC Summary}}, have variously named id parameters.

Note: Some pages occasionally show up here despite having no invalid IDs. This is most likely due to template caching issues. If no ID is obviously problematic, try doing a null edit on the page to see if that fixes the issue.