WP is locking me out of my website

After I activated Akismet, SEO Pack and W3 Cache, I find that I cannot return to my site. I am getting a page that says this:

Warning: ini_set() has been disabled for security reasons in /var/www/vhosts/aceyourweight.com/httpdocs/wp-content/plugins/article2pdf/contributed/fpdi/fpdi.php on line 22

Warning: Cannot modify header information – headers already sent by (output started at /var/www/vhosts/aceyourweight.com/httpdocs/wp-content/plugins/article2pdf/contributed/fpdi/fpdi.php:22) in /var/www/vhosts/aceyourweight.com/httpdocs/wp-includes/pluggable.php on line 890.

Any ideas about what I can do? Thanks!!!