Can anyone help on how to troubleshoot this error message?  I received it after deactivated my message plugin. The plugin did not allow me to adjust the mode for chats,  or chats and direct messages or just inbox messaging.  The setting button was totally missing.  Once I deactivated I received the error message and not cannot access my website.  

Here is the error message.

Fatal error: Class 'MAILBOX_BOL_ConversationService' not found in /home/lenab433/public_html/ow_plugins/discover/classes/event_handler.php on line 36

Thank you.