I'm sorry to hear about your difficulties you are experiencing.
I am also encountering the behavior you have described, and eventually a generic error message, when unchecking the “Show images in active listings.” option on the Image Selection page within your account, but I am uncertain what may be causing this at this time.
However, I confirmed that the issue has already been forwarded to our technical team for further investigation based on the support case you filed on the subject, and we will follow up with you again through that ticket once the issue has been address or any related information becomes available.
Unfortunately, I do not know of any way to work around the issue for the time being, except to refrain from unchecking the “Show images in active listings.” option.
I hope to have some more encouraging news for you soon!