Winbox can not be downloaded by local routerboard. More RB's return error 404 like below.

You probably have some sort of branding or modified webpage on the router. Winbox is not on the router anymore. The link should be going to our download page, unless you have custom HTML files in the router.

You should use Netinstall to re-install your router. Afterwards it will redirect you and download Winbox from our download page.

We did remove Winbox itself from RouterOS so it would not take up space.