Error message after adding twitter widgets

I updated some of my twitter widgets and now my wordpress is messed up. It said i needed to first make an account with Twitter Developers in order for these widgets to work, and when I made an account nothing happened. I tried to delete the widgets and when i selected and deleted them the same error message came up. My website no longer appears on my ipad either.

Does anyone know why this is?

Warning: Cannot modify header information – headers already sent by (output started at /home/content/37/7821237/html/design/wp-content/plugins/twitter-feeder/twitter-feeder.php:1) in /home/content/37/7821237/html/design/wp-includes/pluggable.php on line 876

Thanks!