Problem when publishing normal pages - Warning Cannot Modify Header Information

If you are experiencing an error similar to below when publishing regular WordPress pages and posts:

Warning: Cannot modify header information - headers already sent by (output started at ... /public_html/wp-content/plugins/optimizeMember/includes/classes/admin-notices.inc.php:87) in ... /public_html/wp-includes/pluggable.php on line 1207

This issue has been found to be caused by not having selected a Membership Options page within the OptimizeMember settings. These can be found within OptimizeMember > General Options > Membership Options

Please choose a page for your membership options page (this can be any page for now - we recommend a sales page or login page) and this error will stop.