Back to Error DirectoryW3C EPUBCheck Standard
CHK-006Retailer Warning

Unable to parse the custom format parameter in message overrides fi...

Unable to parse the custom format parameter in message overrides file "resource".

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What This Error Means in Plain English

EPUBCheck detected Unable to parse the custom format parameter in message overrides file "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 CHK-006: Unable to parse the custom format parameter in message overrides file "resource".

Manual Fix Instructions (for Sigil / Calibre)

  1. Locate the file and line flagged under rule CHK-006 in your EPUB editor (Sigil or Calibre).
  2. Apply the required syntax correction matching the CHK-006 specification.
  3. Re-pack and validate with PreFlight EPUB to confirm zero residual errors.