Can't login as admin after installation of Twitter Follow

Hi – I installed Twitter Follow on my site (www.mangetout2012.co.uk) yesterday. Now when I try to access my /wp-admin I get the following message:

Warning: Cannot modify header information – headers already sent by (output started at /home/rnatkiel/public_html/wp-content/plugins/twitter-follow-button-shortcode/FollowButton.php:165) in /home/rnatkiel/public_html/wp-includes/pluggable.php on line 881

I’m unable to even put my email or username in to log in and remove the plugin. I’m not sure how I can get round this, does anyone have any help/suggestions?

http://wordpress.org/extend/plugins/twitter-follow/