Hi @ozgurpolat,
Sorry to hear of the problem you are having.
I could not reproduce the same issue on my test site using the latest version of WP Smush.it plugin.
Could you please try using the browser uploader instead of the multi-file uploader and let me know if that makes a difference for you?
It was working fine before, I don’t know what happened.
Have you added/updated/deleted anything recently on your site that caused this issue?
Does it work for you if you set the WP Smush.it option “Use Smush.it on upload?” to “Do not process on upload” on the following path?
Admin Area -> Settings -> Media -> WP Smush.it
Please try using the solutions posted in the following reply to resolve the issue.
https://www.ads-software.com/support/topic/media-upload-fails?replies=4#post-5662202
Kind Regards,
WPMU DEV
