In event of an error or exception condition, repositories must indicate OAI-PMH errors, distinguished from HTTP Status-Codes, by including one or more error elements in the response. While one error element is sufficient to indicate the presence of the error or exception condition, repositories should report all errors or exceptions that arise from processing the request. Each error element must have a code attribute that must be from the following table; each error element may also have a free text string value to provide information about the error that is useful to a human reader. These strings are not defined by the OAI-PMH.

Version 2 of the OAI-PMH recommends clear separation of OAI-PMH errors and HTTP statuses in a next way:

• all OK at HTTP level? => 200 OK

• something wrong at OAI-PMH level? => OAI-PMH error (e.g. badVerb)

• HTTP codes 302, 503, etc. still available to implementers, but no longer represent OAI-PMH events