Back to Error DirectoryW3C EPUBCheck Standard
PKG-020Critical Ingestion Error

OPF file "resource" could not be found.

OPF file "resource" could not be found.

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Fix all PKG-020 errors in your EPUB automatically

PreFlight checks for PKG-020 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 OPF file "resource" could not be found.. 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 PKG-020: OPF file "resource" could not be found.

Manual Fix Instructions (for Sigil / Calibre)

  1. Locate the file and line flagged under rule PKG-020 in your EPUB editor (Sigil or Calibre).
  2. Apply the required syntax correction matching the PKG-020 specification.
  3. Re-pack and validate with PreFlight EPUB to confirm zero residual errors.