[Plugin: WP Title 2] Plugin stopped working

It worked well for a while but then it just stopped working. I’m building a new website. I made a new post and after I posted it somehow all the posts got the same title. Now all posts have the title of my last post.

I’m using this code in single.php to show the title and subtitle:

<h1 class="main"><?php remove_filter('the_title','wptitle2_the_title',999); the_title(); ?></h1>
<h2 class="sub"><?php add_filter('the_title','wptitle2_the_title',999); the_title(); ?></h2>

I can’t figure out what’s wrong.