"Fatal error: Cannot redeclare limit_login_setup()"

Hi there. I’m getting the following message when I visit my website (both the main page, and the login page):

Fatal error: Cannot redeclare limit_login_setup() (previously declared in /homepages/8/d412612632/htdocs/app412622543/wp-content/mu-plugins/limit-login-attempts.php:97) in /homepages/8/d412612632/htdocs/app412622543/wp-content/plugins/limit-login-attempts/limit-login-attempts.php on line 129

Can someone please tell me what’s wrong? I haven’t made any changes to my site recently, and logged in fine this afternoon. I’ve never seen this before and really can’t have my site down right now 🙁 Please help!!

http://wordpress.org/plugins/limit-login-attempts/