title: AccessError _unknown model
body: <p>I am creating a custom module for Odoo 8 which adds custome fields into res.partner. I've been struggling with some troubles with permissions, but when I finally dealed with them I encountered a new error:</p>
  
  <p><a href="https://i.stack.imgur.com/fSkYa.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fSkYa.png" alt="enter image description here"></a></p>
  
  <p>I seems as if it does not recognise my model...</p>
  
  <p>Here you go my code:</p>
  
  <p><strong>mymodule.py</strong></p>
  
  <pre><code>import openerp
  from openerp.osv import fields, osv, orm
  from openerp import models
  
  class poligono_poligono(models.Model):
      _name = "poligono.poligono"
      _rec_name= "poligono_name"
      _columns = {
          'poligono_name': fields.char('Polígono', required=True),   
  }
  
  class cant_neg_dir(models.Model):  
          _inherit = "res.partner"
          _columns = {
          'dir_poligono_empresa': fields.many2one('poligono_poligono' ,'Polígono'),
  }
  </code></pre>
  
  <p><strong>__openerp__.py</strong></p>
  
  <pre><code>'data': [
          'mymodule.xml',
          'security/mymodule_security.xml',
          'security/ir.model.access.csv',
      ],
  </code></pre>
  
  <p><strong>security/ir.model.access.csv</strong></p>
  
  <pre><code>id,name,model_id/id,group_id/id,perm_read,perm_write,perm_create,perm_unlink 
  access_cant_neg_dir,cant_neg_dir.cantnegdir,model_poligono_poligono,cant_neg_dir.group_name_test_user,1,1,1,1
  </code></pre>
  
  <p><strong>security/mymodule_security.xml</strong></p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;openerp&gt;
      &lt;data noupdate="0"&gt;
          &lt;record model="ir.module.category" id="module_category_name_test"&gt;
              &lt;field name="name"&gt;Directorio&lt;/field&gt; 
              &lt;field name="sequence"&gt;7&lt;/field&gt;
          &lt;/record&gt;
          &lt;record id="group_name_test_user" model="res.groups"&gt;
              &lt;field name="name"&gt;Usuario&lt;/field&gt;
              &lt;field name="category_id" ref="module_category_name_test"/&gt;
              &lt;field name="implied_ids" eval="[(4, ref('base.group_user'))]"/&gt;
          &lt;/record&gt;
          &lt;record id="group_name_test_manager" model="res.groups"&gt;
              &lt;field name="name"&gt;Administrador&lt;/field&gt;
              &lt;field name="category_id" ref="module_category_name_test"/&gt;
              &lt;field name="implied_ids" eval="[(4, ref('group_name_test_user'))]"/&gt;
              &lt;field name="users" eval="[(4, ref('base.user_root'))]"/&gt;
          &lt;/record&gt;
      &lt;/data&gt;
  &lt;/openerp&gt;
  </code></pre>
  
  <p>Thank you very much in advance for your help!</p>
  
  <p>Kind regards.</p>