Issues with Flexible Frontend plugin

Hi!

I installed this plugin that was supposed to create a log in box at my site (I’m using marketpress for multisite):

http://wordpress.org/plugins/flexible-frontend-login/

I’m also seeing this error message at my dashboard:

Notice: Undefined index: html_block in /home/wheelofcommerce/wheelofcommerce.com/wp-content/plugins/flexible-frontend-login/includes/options-page.php on line 243

Warning: Cannot modify header information – headers already sent by (output started at /home/wheelofcommerce/wheelofcommerce.com/wp-content/plugins/flexible-frontend-login/includes/options-page.php:243) in /home/wheelofcommerce/wheelofcommerce.com/wp-includes/option.php on line 747

Warning: Cannot modify header information – headers already sent by (output started at /home/wheelofcommerce/wheelofcommerce.com/wp-content/plugins/flexible-frontend-login/includes/options-page.php:243) in /home/wheelofcommerce/wheelofcommerce.com/wp-includes/option.php on line 748

How do I fix it?

Thanks.