Can't access WordPress login page! Help!!

Hello, I can’t access my wp-admin screen. Instead whenever I try acessing it I’m greeted with this message; Warning:

Cannot modify header information – headers already sent by (output started at /home/theace/public_html/howtorideyourman.com/wp-content/plugins/embed-selected-posts-in-page/templatemaker.php:1) in /home/theace/public_html/howtorideyourman.com/wp-includes/pluggable.php on line 881

I’m guessing this has something to do with my theme as I have been getting weird messages similar to this while working in wordpress. Its a “Page lines” theme.