Can´t set front page display static page in Product theme


I am using Product Theme on WP3.0 Mulite User, Buddypress 1.2.5. I have alreadys created a page "blog" with the blog template. Now I want to change the default display in the reading settings to "front page display" --> "static page" and pick the page "Blog" to display as front page. But for some reason the change ist not applied. When I try to safe the change it just "jumps back".

Any help for that one?

Greetings from Germany