Error "Invalid response from server"

The error message "Invalid response from server" can sometimes be puzzling, especially if the image actually exists and looks good in a browser.

Check the response output

If you get this error message, it may be that some output from another plugin (or a notice/warning) is corrupting the JSON responses from our plugin's AJAX calls. To see this output, do the following:

  1. Go to Media > Bulk ShortPixel.
  2. Start optimizing your images (if you have not already).
  3. Open your browser's developer tools (usually F12 on Windows, or Option+⌘+' on macOS).

Proceed as shown in the screenshot:

  1. Click on the Network tab.
  2. Select the XHR filter.
  3. Click on any admin-ajax.php?_fs_blog_admin=true request.
  4. Select the Response tab. What you see in the screenshot is the correct AJAX call.

If you don't see something similar, we recommend you to try to search for the plugin in question:

  1. Deactivate all plugins except ShortPixel.
  2. Activate the plugins one by one. After each individual activation, try the bulk optimization again until you find the plugin that is curropting the JSON responses.

Check if your server is overloaded

If the above measures did not help, it's possible that your server has limited capacity in terms of processing power and memory. Some of ShortPixel's features may require more resources than others, so you may experience server overload. You can try temporarily disabling the following functions.

  • Convert PNG images to JPEG
  • Optimize Retina images
  • Optimize other thumbnails

If you have a lot of thumbnails, you can try excluding some of them from optimization, as each thumbnail (and its WebP + AVIF counterpart) increases server load. You can learn how to do that in this article: How can I optimize only certain thumbnail sizes?

For more information, see this article: My website seems to be slower, could this be because of ShortPixel Image Optimizer?

Other common problems

If you still can not figure out what's going on, please take a look at Why some of the images and/or thumbnails cannot be optimized?

Contact your hosting provider

As a last resort, we recommend that you  contact your hosting provider to find out why our plugin cannot access your images.

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