Please upgrade to 2.2 here.
The 2.0 and 2.1 branches are no longer being updated.
I've been working on a site for a while, and five minutes before release I noticed the "Mark all viewed" plugin doesn't work. When clicking "Mark all viewed" in the sidebar, you're simply redirected back, and none of the posts are marked as read.
The data is imported from a phpbb3 forum, so maybe that's what's causing it?
I hope you guys can help me out with this, or at least tell me why it isn't working.