I was trying to upload a Chrome Extension for my work, and I encounter this problem the whole morning, trying to get help but cannot find much, from the error of upload? url I was thinking it was related to server error…
A few refresh even lead me to error pages like:
Took me a very long time to look for solution, it turns out the problem was in the zipped archive there was a hidden Thumb.db inside and this is the reason why the upload was not successfully.
A bit of a nagging to Google, please AT LEAST provide some kind of error message instead of a loading forever screen, and some (failed) error in developer console.