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OPF-060: duplicate ZIP entry inside the EPUB

Plain English meaning

The EPUB ZIP package contains the same internal file path more than once. EPUB readers and validators need each internal file path to be unique.

Why it happens

• The EPUB was repacked incorrectly.
• A ZIP tool appended files instead of replacing old ones.
• A repair attempt left two copies of the same internal path.

What you can check yourself

Many normal ZIP viewers hide duplicate entries, so this error can be confusing. EPUBCheck may be more reliable than the visual file list. If the same path appears twice in a low-level ZIP listing, one copy must be removed and the EPUB rebuilt.

What can usually be fixed

If the duplicate file is truly identical or one copy is obsolete, this can often be fixed by rebuilding the EPUB package with one clean copy of each path.

What cannot be promised

If the two entries are different, someone must decide which version is correct. If that decision depends on book content or layout preference, it may need the author or formatter.