Delete original images get 500 internal server error

After optimizes several images, i want delete the original ones, so i go Tools, EWWW Image Optimizer and press the button.
When WordPress scales down large images, it keeps the original on disk for thumbnail generation. You may delete them to save disk space.
The next pages show how many images should be deleted, but never move.
In the console say:
Failed to load resource: the server responded with a status of 500 (Internal Server Error)
/wp-admin/admin-ajax.php:1
There is a way to fix this?
Thanks.