Last time I looked Bravenet explicitly stated that frames were not supported.

There are two reasons for this.
1. Every frame gets an ad which just makes your site look like sh*t.

2. The way in which the ads are inserted means that if you are too lazy to create a noframes section nothing will display at all.

I remember Courtnie saying one time as well when posting in the forum that frames were NOT SUPPORTED with the free hosting/subdomain

so you have to upgrade your hosting if you want to use frames