Robin Image Optimizer - Optimization Errors and How to Fix Them
When Robin Image Optimizer cannot optimize or convert an image, it saves an error for that image. You see the errors in two places:
- Robin Image Optimizer > Optimize: the images could not be optimized box groups the failed images by reason. Open a reason to see its images, what to do, and a Learn more link to the section of this page.
- Media > Library (list view): the Robin column shows the error of each image.
Some errors fix themselves. Robin tries the image again after 10 minutes, 30 minutes and 2 hours, 5 times at most. Other errors need an action from you. Each section below tells you which.
In this article
Before you contact support
- Go to Robin Image Optimizer > Optimize and open the images could not be optimized box.
- Click Copy diagnostics. Robin copies a text report to your clipboard: the plugin, WordPress and PHP versions, the PHP memory and time limits, the WP-Cron and loopback status, the uploads folder, your main settings, the last error of the optimization server, and the last 20 failed files.
- Paste the report in your support request.
The report does not contain your license key, passwords or tokens.
Problems with the image file
File not found
What it means: The image file is no longer on your server. A plugin, a cleanup tool or a manual delete removed it, but the attachment is still in the Media Library.
What to do: Upload the image again, or delete the attachment from the Media Library.
Damaged image file
What it means: The file is damaged. For example, the upload stopped before the end, or a tool wrote bad data into it. Robin checks each JPEG, PNG, GIF and WebP file before the upload. A damaged file is not sent, so it does not use your quota. The optimization server can also find a damaged file.
What to do: Open the image in an image editor and save it again, or export it again from the original source. Then upload it again, or replace the image. Robin does not try a damaged file again in a bulk run. After you replace the file, click Optimize in the Media Library column.
Missing image metadata
What it means: WordPress has no metadata (size and file name) for the image. The file can be damaged, or the upload did not finish.
What to do: Upload the image again. A plugin that regenerates thumbnails can also create the metadata again.
Unsupported file type
What it means: The optimization server does not support this type of file. The file name can say .jpg, but the data inside is another format.
What to do: Convert the file to JPEG, PNG, GIF or WebP in an image editor, then upload it again.
Plan and license limits
File exceeds the plan size limit
What it means: The file is larger than the largest file your plan accepts. The free plan accepts files up to 10 MB. Robin checks the size before the upload, so the file is not sent.
What to do: Do one of these:
- Turn on Resizing large images in Robin Image Optimizer > Settings. Robin then makes the original smaller before the upload.
- Make the image smaller before you upload it.
- Upgrade your plan.
Robin tries these images again when your plan changes.
Image exceeds the plan pixel limit
What it means: The image has more pixels (width × height) than your plan accepts.
What to do: Turn on Resizing large images, make the image smaller before the upload, or upgrade your plan.
Format is not in your plan
What it means: Your plan does not include this output, for example AVIF on the free plan.
What to do: Upgrade your plan, or turn off that format in Robin Image Optimizer > Settings.
License not recognized
What it means: The optimization server does not know your license key. The key is wrong, expired, or was activated on another site.
What to do: Go to Robin Image Optimizer > License. Make sure that the key is active. Deactivate it and activate it again if needed. Robin sends nothing until the license works, so no image uses a retry.
Optimization server problems
These errors come from the connection to the optimization server, or from the server itself. Most of them fix themselves: Robin tries the images again later.
Too many requests
What it means: Your site sent too many requests in a short time. The server asked Robin to wait.
What to do: Nothing. Robin waits for the time that the server asked for, then continues. Bulk runs show a wait and continue on their own.
Optimization server in maintenance
What it means: The optimization server is busy or in maintenance.
What to do: Nothing. Robin waits and continues later.
Optimization server error
What it means: The optimization server had an unexpected error with this image.
What to do: Nothing at first: Robin tries again later. If the same image fails after all retries, click Copy diagnostics and send the report to support.
Invalid server response
What it means: The answer of the optimization server was not complete or not valid. A proxy or a firewall between your site and the server can change the answer.
What to do: Robin tries again later. If it happens again, send the diagnostics to support.
No answer from the server
What it means: The optimization server did not answer for this file in time.
What to do: Robin tries again later. If it happens often, ask your host if a firewall limits outgoing requests.
Optimization failed
What it means: The optimization server could not optimize this image.
What to do: Robin tries again later. If the image fails after all retries, send the diagnostics to support.
Optimization server unreachable
What it means: Your server cannot connect to the optimization server. A firewall, a DNS problem, or the WP_HTTP_BLOCK_EXTERNAL constant can block the request.
What to do: Ask your host to allow outgoing HTTPS requests to dashboard.robinoptimizer.com. If you use WP_HTTP_BLOCK_EXTERNAL, add that host to WP_ACCESSIBLE_HOSTS.
Optimization server error (HTTP status code)
What it means: The optimization server, or a proxy before it, answered with an HTTP error code and no explanation.
What to do: Robin tries again later. If it happens again, send the diagnostics to support. The report has the code and the request ID.
Download failed
What it means: The server optimized the image, but your site could not download the result.
What to do: Nothing. Robin tries again later. If it happens often, ask your host if a firewall limits outgoing requests.
Invalid download
What it means: The downloaded file is not the optimized image, for example an error page of a proxy.
What to do: Nothing. Robin tries again later.
Server limits on your site
PHP time limit reached
What it means: The request was near the PHP time limit (max_execution_time). Robin stopped the image before PHP stopped the request.
What to do: Do one of these:
- Ask your host to raise
max_execution_timeto 60 seconds or more. - In Robin Image Optimizer > Settings, lower Images per iteration.
Robin tries the image again later.
PHP memory limit reached
What it means: The optimization of this image used all the memory that PHP allows (memory_limit). Large images need a lot of memory, for example to make a backup or to resize.
What to do: Ask your host to raise the PHP memory_limit to 256 MB or more. You can also set WP_MAX_MEMORY_LIMIT in wp-config.php. Or make the image smaller before you upload it. Then click Optimize in the Media Library column.
The PHP process stopped
What it means: The optimization of this image stopped the PHP process several times. The cause is usually the PHP memory limit or the time limit. Robin stops trying the image so that it does not stop the other images.
What to do: Ask your host to raise the PHP memory_limit and max_execution_time, then click Optimize on the image. If the image still fails, send the diagnostics to support.
Backup failed
What it means: Robin could not save the backup of the original file. The uploads folder, or the wp-content/uploads/wio_backup folder, is not writable.
What to do: Ask your host to make the uploads folder writable for the web server. Or turn off Backup images in Robin Image Optimizer > Settings if you do not need backups.
Optimized file not saved
What it means: Robin could not write the optimized file over the original. The folder or the file is not writable.
What to do: Ask your host to make the uploads folder writable for the web server.
Outside the allowed folders
What it means: The file is outside the folders that this site can change. On a multisite network, a site cannot change the files of another site.
What to do: On a network, ask a super admin to optimize the file.
Unexpected error
What it means: A PHP error stopped the optimization.
What to do: Turn on Enable error log in Robin Image Optimizer > Settings. Optimize the image again. Then send the error log and the diagnostics to support.
Failed in an earlier version
What it means: The image failed in an earlier version of the plugin.
What to do: Click Optimize on the image to try again with the current version.
Skipped WebP and AVIF files
These are not errors. Robin did not keep a WebP or AVIF file for a good reason. The original image is still optimized and served.
Not smaller than the original
The WebP or AVIF file was not smaller than the optimized original, so Robin kept the original. Nothing to do.
Already in this format
The file is already a WebP or AVIF file. Nothing to do.
Animated image
Animated images keep their format. Nothing to do.
GIF image
GIF images are optimized, but not converted to WebP or AVIF. Nothing to do.
Too large for the format
The image is too large for this format, for example for AVIF. Make the image smaller if you need this format for it.
Background optimization and WP-Cron
Background optimization cannot be turned on
What it means: Background optimization (Pro) needs a request from your site to itself (a loopback request to admin-ajax.php). Robin tests this request before it saves the setting. The message says why the test failed, for example an HTTP status code or a connection error. A security plugin, HTTP authentication or the firewall of the host can block the request.
What to do: Do one of these:
- Allow requests from the site to its own
wp-admin/admin-ajax.php, then save the setting again. - Keep Scheduled optimization.
- Let a system cron job run the queue without a loopback request:
wp robin queue run.
WP-Cron does not run on this site
What it means: WordPress events are more than an hour late. Scheduled optimization and the optimization of new uploads wait. This happens when DISABLE_WP_CRON is set in wp-config.php and no system cron job runs WP-Cron, or on a site with no visits.
What to do: Ask your host to add a system cron job that calls wp-cron.php every 5 minutes, or that runs wp robin queue run (Pro, WP-CLI).