what does this mean!! :(

Warning: Cannot modify header information – headers already sent by (output started at /home/cxs410/public_html/wp/wp-content/plugins/mostwantedposts.php:28) in /home/cxs410/public_html/wp/wp-admin/admin.php on line 6

This is showing up in my wordpress dashboard.. i know that it is caused my the mostwantedpost plugin.. but i don’t know why.. it say’s line 6,7,8 and 9 and messed.

-Chris