Not working. Options Page shows up, but after "save," 404.

I installed WP Native Dashboard, but I am having some pretty strange problems. After installation, the only thing that is there is in the “Options” part of WP. There is no language selector/indicator in the top left. When I try to change the options, I get a 404 page not found.

Any help would be great.

http://wordpress.org/extend/plugins/wp-native-dashboard/