This is certainly the first time I experienced this. Not sure why. I have tried to use different web browsers.
Incident ID:6529d14d3d3e9
It weird that I was able to upload another image after the error
Did this happen just once, or several times with the same file?
This error usually occurs when a new upload is attempted but the browser did not correctly reload the page.
When you click on the "New Upload" button, what you are doing is refreshing the page, it will be the same as clicking "F5". Sometimes this refresh may not occur, generating this error.
What I recommend, if you are doing several uploads in a row, is instead of clicking the "New Upload" button, you will sometimes click "F5", to ensure that the page is actually refreshed.