There is a conflict between the Twenty Twelve WordPress and the All in One SEO Pack plugin. When the plugin is installed and you happen to be using the Twenty Twelve theme, the result is, there will be no space between your site title and blog title. You’ll notice this if you look at the title bar of your browser. After a couple of searches, I found a fix online. It involves editing the Twenty Twelve functions.php file and commenting out line 185 which contains the code below.
You will need to change:
add_filter( 'wp_title', 'twentytwelve_wp_title', 10, 2 );
and comment out:
// add_filter( 'wp_title', 'twentytwelve_wp_title', 10, 2 );
Also, you need to clear your browser cache to see results.