When a URL is not accessible for upload-by-url, you get:
Upload warning
An HTTP error occured: HTTP/1.0 403 Forbidden
The latter in big red letters. That error is not particularly userfriendly. First it does not state WHERE the HTTP error occurred. Nor does it explain very well the consequence of the error.
Something like
Upload warning:
File could not be retrieved from url 'theurl', because (server does not allow it|missing file|unreachable server|whatever)
Please try to download the file yourself and then upload the file from your own computer, instead of using the url to upload.
anything more momproof than "HTTP/1.0 403 Forbidden" will do however :D
Version: unspecified
Severity: enhancement