answer. :) - consider being more specific / understandable.

Can you paste your code where getting this error

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
 <record model="ir.ui.view" id="res_partner_endoattachment_sys_info">
     <field name="name">ir.attachment.multiple.model</field>
    <field name="model">res.partner</field>
     <field name="priority" eval="20"/>  
    <field name="view_type">tree,form</field>    
    <field name="inherit_id" ref="crm_sys_info.res_partner_sys_info"/>
     <field name="arch" type="xml">
    <xpath expr="//field[@name='room_lines']" position="replace">
    <field name="room_lines" nolabel="1" widget="twotomany" attrs="{'invisible': [('is_company','=', True)]}" >
       
                        <form string="Room" version="7.0" position ="replace">

                         <group>
                             <group>
                               <field name="name" />
                              <field name="remote_conn_room" placeholder="Put Remote connection details here..."  colspan="4"  />
                            </group>
                         </group>

                        <group col="6" colspan="2" string="Speciality"  >
                        <field name="licensce_lines" widget="one2many"  nolabel="1">
                                <tree string="License" editable="bottom"  colors="red:deactive == True ;red:support_end &lt; current_date  &lt;  installed_date">
                                    <field name="name"/>
                                    <field name="exe_version" />
                                    <field name="comp_name"/>
                                    <field name="lic_name" invisible="1"/>
                                    <field name="installed_date"/>
                                     <field name="support_start" />
                                    <field name="support_end" />
                                    <field name="comments" />
                                    <field name="deactive"/>
                                </tree>
                        </field>
                        </group>
                        <group col="6" colspan="2" string="Cables" >
                            <field name="cableing_lines" widget="one2many" nolabel="1">
                            <tree string="Cables" editable="bottom">
                                <field name="name"/>
                                <field name="serial_num" />
                                <field name="cable_length" />
                                <field name="installed_date"/>
                                <field name="comments"/>
                            </tree>
                            </field>
                        </group>
                        <group col="6" colspan="2" string="Custom Cabling" >
                            <field name="cust_cable_lines" widget="one2many" nolabel="1">
                            <tree string="Custom Cables" editable="bottom" >
                                <field name="name" />
                                <field name="length" />
                                <field name="communication"/>
                                <field name="comments"/>
                            </tree>
                            </field>
                        </group>

                          <group col="6" colspan="2" string="Video Processors">
                            <field name="video_process_lines" widget="one2many" nolabel="1" >
                            <tree string="Video Processors" editable="bottom">
                                <field name="name"/>
                                <field name="type_id"/>
                                <field name="comm_id"/>
                                <field name="comments"/>
                            </tree>
                            </field>
                        </group>
                        <group col="6" colspan="2" string="Other Equipment"  >
                            <field name="other_equp_lines" widget="one2many" nolabel="1" >
                            <tree string="Other Equipment" editable="bottom">
                                <field name="name" />
                                <field name="type_id" />
                                <field name="comm_id"/>
                                <field name="comments"/>
                            </tree>
                            </field>
                        </group>
                       <group col="6" colspan="2" string="Additional Notes" >
                         <field name="notes" placeholder="Put additional notes on the room.."/>
                       </group>
            
        <group col="6" colspan="2" string="Attachments">      
          <field name="attachment" widget="many2many" />   
        </group>

                        </form>

          
                  </field>    
                 
      </xpath>    
    
    </field>
 </record>

    </data>
</openerp>

In py file
##############################################################################

from openerp.osv import osv, fields
from collections import Counter
from openerp.tools.translate import _
from datetime import date, datetime, timedelta
import time

    
class document_file(osv.osv):
    _inherit = 'room.lines'  
    _columns = {
    'attachment': fields.many2one('ir.attachment','Attachments'),
}