This error will appear on products after Zentail sends a feed to Amazon and Amazon is not able to upload the image of the product due to another product listing error. Oftentimes this error will mean that your product is listed on Amazon, however, new images will not be able to update to Amazon.
To solve this error, here are some troubleshooting tips:
Double check your product's data in Zentail and make sure that the data looks correct.
Since this error can appear in product groups, check each sku in the product group and make sure that none of the skus in the group have an error. If you see an issue, be sure to correct it and save the sku.
Once the product/product group appear to be correct, click Update on Advanced Options for Amazon to send a new product feed to Amazon.
For more advanced tips on ascertaining product group accuracy, check out this article here on how to audit your product groups.