Plugin Crashes Site

Here’s what I am getting when I activate this plugin:

Warning: Cannot modify header information – headers already sent by (output started at [site]/wp-content/themes/PureType/page-full.php:7) in [site]/wp-includes/pluggable.php on line 1121

Love this idea – protect pages without a full-blown membership plugin. Hope we can get it to work.

https://wordpress.org/plugins/wp-require-login/