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NCX-001Critical Ingestion Error

NCX identifier ("resource") does not match OPF identifier ("resourc...

NCX identifier ("resource") does not match OPF identifier ("resource").

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Fix all NCX-001 errors in your EPUB automatically

PreFlight checks for NCX-001 issues in memory and provides 1-click remediation during client-side packaging.

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What This Error Means in Plain English

EPUBCheck detected NCX identifier ("resource") does not match OPF identifier ("resource").. Digital reading systems and bookstores require standard conformance to ensure compatibility across all reading apps.

Why Retailers & EAA Regulations Block This File

Automated book distributors (Apple Books, Amazon KDP, Kobo, and IngramSpark) run strict EPUBCheck validation on ingest and reject non-compliant files.

Technical Specification: W3C EPUBCheck rule NCX-001: NCX identifier ("resource") does not match OPF identifier ("resource").

Manual Fix Instructions (for Sigil / Calibre)

  1. Locate the file and line flagged under rule NCX-001 in your EPUB editor (Sigil or Calibre).
  2. Apply the required syntax correction matching the NCX-001 specification.
  3. Re-pack and validate with PreFlight EPUB to confirm zero residual errors.