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Troubleshooting Common NextGEN Gallery Errors with PHP 8.0 and Above

39 threads Sep 9, 2025

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Many users of the 'Photo Gallery, Sliders, Proofing and Themes – NextGEN Gallery' plugin have encountered a range of errors after updating their websites to use PHP 8.0, 8.1, or 8.2. This guide will help you identify and resolve the most common issues, allowing you to benefit from the performance improvements of newer PHP versions while maintaining a functional gallery.

Why Do These Errors Occur?

The core of the problem lies in PHP's stricter type handling and deprecated features in versions 8.0 and above. Code that worked without warnings in PHP 7.4 may now throw fatal errors or TypeError exceptions. The 'Photo Gallery, Sliders, Proofing and Themes – NextGEN Gallery' team has been working to address these compatibility issues in recent updates, but some conflicts and edge cases may still occur, especially with specific server configurations or when other plugins are active.

Common Errors and Their Solutions

1. TypeError: array_filter(): Argument #1 ($array) must be of type array, bool given

Where it happens: Often occurs when managing albums or viewing WordPress admin pages like Posts or Pages.
Potential solution: This error suggests a function is receiving a boolean (true/false) value when it expects an array. A common workaround reported by users is to temporarily revert to PHP 7.4 if possible. However, the preferred long-term fix is to ensure you are running the latest version of the NextGEN Gallery plugin, as many of these compatibility issues have been addressed in updates released after late 2023.

2. TypeError: Cannot access offset of type string on string

Where it happens: Frequently triggered when using the "Scan Folder for New Images" utility or other gallery management tasks.
Potential solution: This error indicates the code is trying to access a string variable as if it were an array. Users have found that uploading images directly through the WordPress media library or the NextGEN admin interface often works without error, whereas adding files via FTP and then scanning can cause this problem. If you must use FTP, try adding a single, small image and scanning to see if the error persists.

3. Fatal Error: Uncaught Error: Class "C_Gallery_Storage" not found

Where it happens: This is typically a conflict with another plugin, most commonly noted with Imagify.
Potential solution: The first step is to perform a conflict test. Temporarily deactivate all other plugins except NextGEN Gallery and switch to a default WordPress theme (like Twenty Twenty-Four). If the error disappears, reactivate your plugins one by one to identify the culprit. Contact the support for the conflicting plugin and inform them of the compatibility issue with NextGEN Gallery and newer PHP versions.

4. Fatal Error: Cannot declare class M_Attach_To_Post

Where it happens: This error prevents access to the WordPress admin area after a plugin update.
Potential solution: This error suggests a class is being declared twice. Access your site via FTP or your host's file manager and rename the /nextgen-gallery/ plugin folder. This will deactivate the plugin and allow you to log into your WordPress admin. Then, rename the folder back to its original name and ensure you are installing the latest, correct version of the plugin, checking that no duplicate copies exist.

5. Fatal Error: Unsupported operand types: string * int

Where it happens: Often related to display types, specifically in slideshow or thumbnail galleries, when a parameter like gallery_height="auto" is used in a shortcode.
Potential solution: Modify the problematic shortcode. For example, change gallery_height="auto" to a specific integer value like gallery_height="400". Avoid using non-numeric values for dimensional parameters in shortcodes when using PHP 8.2.

General Troubleshooting Steps

If you encounter an error not listed above, follow these steps to diagnose the problem:

  1. Update Everything: Ensure WordPress, your theme, and all plugins (especially NextGEN Gallery) are updated to their latest versions. The 'Photo Gallery, Sliders, Proofing and Themes – NextGEN Gallery' team has resolved many PHP 8.x issues in recent releases.
  2. Enable WP_DEBUG: Temporarily enable debugging by adding define( 'WP_DEBUG', true ); to your wp-config.php file. This will provide more detailed error messages, which are crucial for identifying the root cause. Remember to disable it afterwards.
  3. Conflict Test: As mentioned above, deactivate all other plugins and use a default theme. This is the most effective way to determine if the error is due to a conflict with another piece of software on your site.
  4. Check PHP Version: While updating the plugin is the goal, if a critical issue persists, a temporary rollback to PHP 7.4 can restore functionality while you seek a more permanent solution. However, be aware that PHP 7.4 has reached end-of-life and is not recommended for long-term use.

By following this guide, you should be able to resolve the most common NextGEN Gallery errors associated with PHP 8+. For persistent, unique issues, searching for the specific error message on independent troubleshooting forums often yields helpful community-driven solutions.

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