Probably THE most annoying error in WordPress. Mainly because it’s so non-descriptive and proffers nothing so you can try and solve the issue.
I’m not entirely sure why it happens. I’ve used WordPress for nearly 9 years and have seen it on and off in the last 4 maybe. Normally it goes away of it’s own accord or re-uploading the image does the trick but with last update of WordPress it did not.
It may be a hosting issue relating to the graphics library used with WordPress, to be honest I haven’t looked into it in huge depth but I did uncover I nifty solution that worked in my case. I added the following to functions.php
add_filter( 'wp_image_editors', 'change_graphic_lib' ); function change_graphic_lib($array) { return array( 'WP_Image_Editor_GD', 'WP_Image_Editor_Imagick' ); }
Hopefully it works for you too!