It appears that Apple moved the Error Handling Programming Guide to this URL:
https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/ErrorHandlingCocoa/ErrorHandling/ErrorHandling.html
Apple also moved the Incremental Store Programming Guide to this URL:
https://developer.apple.com/library/content/documentation/DataManagement/Conceptual/IncrementalStorePG/Introduction/Introduction.html
Apple also moved the Predicate Programming Guide to this URL:
https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/Predicates/AdditionalChapters/Introduction.html