This seems to be a signature/hash error, probably because the portable version number jumped from 6.0.23 to 6.0.26, whereas the official Zotero released 3 versions in 2 days (see https://www.zotero.org/support/changelog).
So please fix it & re-upload. Many thanks.
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PortableApps.com Platform
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The downloaded copy of Zotero Portable is not valid and can not be installed. This could be due to an incomplete download or other network issue. Please try running the updater again when complete.
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I'd neglected to update the hash when I posted. It's fixed now. Sorry for the inconvenience and thanks for letting me know.
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