got some error messages in header

After installing the membership plugin, I got this message in the header; "Warning: Cannot modify header information - headers already sent by (output started at /home/content/25/11665725/html/site/wp-content/plugins/directory/core/custompress/core/content-types.php:1) in /home/content/25/11665725/html/site/wp-content/plugins/mainwp-child/mainwp-child.php on line 10

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/content/25/11665725/html/site/wp-content/plugins/directory/core/custompress/core/content-types.php:1) in /home/content/25/11665725/html/site/wp-content/plugins/comments-plus/lib/external/facebook/facebook.php on line 49

Warning: Cannot modify header information - headers already sent by (output started at /home/content/25/11665725/html/site/wp-content/plugins/directory/core/custompress/core/content-types.php:1) in /home/content/25/11665725/html/site/wp-includes/pluggable.php on line 899"

Have tried to disable the latest installed plugins, but nothing changed. Also tried to delete the child temify plugin By John P. Bloch via the dashboard, but that wasn´t possible. Any advice please?