Can't login – Help!

I’m unable to login to wordpress. I launch a new page, type in my usual yourstie.com/wp-admin/ and I get taken to an error message that says.

Warning: Cannot modify header information – headers already sent by (output started at /home/rocnuts/public_html/wp-content/plugins/youtube-channel-gallery/youtube-channel-gallery.php:1) in /home/rocnuts/public_html/wp-includes/pluggable.php on line 881

The front page of my site gets the same error message.

The strangest thing is, the rest of my site works and when the site is already open I can click through to the home page and it loads.

Can someone please offer a solution???

Crossing my fingers for a response.

Scott