_inherit = ['mail.thread', 'ir.needaction_mixin'] you must add this line to your *.py class.. and thats all .

The object ceg.visitor doesn't sound like a regular object.

The message is about an object missing an attribute or method. So there is an object of type ceg.visitor, and in the code it wants to use message_post (either to perform something, like posting a message to or from that object, or it wants to check/fill the variable message_post).

Have you installed any code from internet or made by yourself/your company? In these cases, check the code, and make sure there is no error in the code (wrong object name, or mistyped method) and make sure that the object ceg.visitor has either a method message_post, or a variable (that is field) with that name.