Error – The incident ID is: 0

I recently ran into an error that occurs any time I try to place an image into a page or post. Whenever an image is placed and I try to update/publish the page/post, I am redirected to a page which displays an Error message. The phrase “CHANGE ME!” flashes on and off, and below this the message “The incident ID is: 0.”

I have been running my site for quite some time now, and images were working fine up until last night. The weird part is that I haven’t added, updated, or changed anything that would appear to cause this error. Here’s what I have already tried:

1. Disabled all plugins.
2. Changed the theme.
3. Tried creating a new page and post.

None of these have worked. Thank you in advance for help with this!