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Most issues we see are triggered by a plugin conflict. Please ensure there is no plugin conflict by temporarily deactivating all plugins, reactivate NextGEN Gallery (and NextGEN Pro/Plus if you have those installed as well) only and confirm if the error persists. If it does not and the error is gone, reactivate each of the other plugins one at a time to locate the culprit.
If there is no plugin conflict, in some rare cases there will be a conflict with a theme. To test this, please temporarily switch your theme to a WordPress default theme. Clear the browser cache and reload the page with the error to confirm if the error is resolved.
Is this issue showing up in all or only some browsers?
If you also have a caching plugin installed, be sure to purge/delete all site cache.
From your WordPress dashboard, go to Tools > Site Health > Info. Click "Copy site info to clipboard" and paste the info here. If you don’t see a Site Health section, you may need to upgrade WordPress. For now, go to Gallery > Overview > Site Details, copy the server information and paste that here.
If you're including a shortcode please be sure to put spaces after the [ and before the ]
Accepted file types: jpg, png, Max. file size: 2 MB, Max. files: 5.
Drop files here or
Screenshots are a huge help! Try a browser extension or free apps like Jing, Owely, Monosnap. 2MB limit per image with a max of 5 files.
Preferably a link to the page where error is shown.
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