This message results from a check before downloading the file.
“HEAD” means the client (here LO) queries the server for various information about the file (the response contains among other things the file size). The server reported “403” meaning you have not the rights to access the directory in which the file is stored.
If you succeed with another machine, then this machine probably sends some credentials with the request. As suggested by @Vanadium, try to download it on your computer from a browser. In a browser you can control more easily credentials than in LO. A URL has the general form
scheme is http, https, ftp, ftps, … If no
user is sent, you can only acces “public” unprotected files. It is not necessary to send your
passwd in the URL (it may be unencrypted), it will be sollicited if needed.