You are trying to use, a wrong ID to browse/write etc in a object, So have a look at your code

I got this error, and after some trace I found that I'm trying to access a field that is not defined in the object I'm dealing with.

I got the case when I tried to override the mail_message.create method. This method is called from several classes. I wrote the following line of code

            ticket_o = self.pool.get('ticket.ticket').browse(cr, uid, val['res_id'])

            if ticket_o.section_id and ticket_o.section_id.email_server:

..........

it crashed in the 2nd line. In trace I found that it acts with the res.partner object not with ticket.ticket one, where res.partner does not have a section id field