The codes people paste into support mail, with the steps that clear them. Each page lists the causes we have actually seen, in the order worth trying.
How the codes are described
A page here is written for the code as an application reports it, which is not the same as a cause. The same number can arrive from a permission check, a missing volume or a file that moved, and the page lists those separately rather than picking one and calling it the answer.
Where a fix is given, the library has seen it work on a file someone sent in. Where nothing has been confirmed, the page says so. Codes are added when someone reports one, which is why the count grows slowly and why some pages are short.