apparently certain mimetypes can’t be uploaded without a plugin or editing the file whitelist (i’m looking for this inside my site).
PJW Mime Config allows you to add / edit mime-types.
Author: Peter Westwood
This plugin allows you to configure extra mime-types for support by the inline-uploader.
A new options page is added as Options … Mime-types which allows you to add/delete the extra mime-types.
I needed to add .ogv support for the html5 <video>