This error can be caused by a large number of deleted repository records appearing at the beginning of an OAI server response to the &verb=ListRecords command. You can test this by running the command <OAI server base URL>?verb=ListRecords&metadataPrefix=oai_dc
in your browser.
If you see entries with <header status="deleted"> in them then this is likely the issue. Contact OCLC Support with your Institution name, repository URL and the collection name that is experiencing the issue to get it fixed.