This is actually the error I get when I activate the plugin, from my Nginx logs:
[error] 11837#0: *38246 FastCGI sent in stderr: "PHP message: PHP Fatal error: Class 'GHEADER_Plugin' not found in /var/www/example.com/public_html/ow_plugins/gheader/init.php on line 14" while reading response header from upstream, client: xxx.xxx.xx.xx, server:
www.example.com, request: "POST /base/ping/index/ HTTP/1.1", upstream: "fastcgi://unix:/var/run/php5-fpm.socket:", host: "
www.example.com", referrer: "
https://www.example.com/admin/plugins/index"
Every time I activate the plugin, it causes the site to crash with a 500 error, then after deactivating the plugin, I cannot access groups. It only happens when trying to enter a specific group's link, and it will redirect to the 500 error page within the site. This can't be fixed until I uninstall the groups plugin and reinstall. Trying to activate a clean install of the group cover plugin reproduces this every time.