This is very strange. I am having the same issue but I am not running WordPress on my site. I came across this from searching the error in Google. I have a form for my client to fill out to change content and upload images. I am using the ckeditor but that stopped working and when you try to upload an image, the page says:
“The requested URL was rejected. If you think this is an error, please contact the webmaster.
Your support ID is: 5378948895080717071″
