BuddyPress.org

It is a rather important bit of information the server platform Apache and IIS have different approaches to rewrite capability, you may need to speak to your hosts and explain that you need some form of url rewriting for your site.

This WP Codex page gives some detail on IIS and permalink structures and rewriting.

https://codex.wordpress.org/Using_Permalinks

This is essentially an issue resting with the core app WP rather than BP