I was just able to edit a gallery post from 2018 and add an additional image to it without any errors on a stock v774 install; do you have any 3rd party modifications or JavaScript that could be stopping the UBB.threads JavaScript from loading?

Note that nothing in the Gallery system has changed from v773 to v774.

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UBB.threads: UBBWiki, UBB Styles, UBB.Sitemaps
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