Can't adapt account.analytic.account type

I am passing in the account.analytic.account field from the sales order for invoicing. the intent is to pass the field when confirming a sales order.

def _prepare_invoice(self, cr, uid, order, lines, context=None):
    """Prepare the dict of values to create the new invoice for a
       sales order. This method may be overridden to implement custom
       invoice generation (making sure to call super() to establish
       a clean extension chain).

       :param browse_record order: sale.order record to invoice
       :param list(int) line: list of invoice line IDs that must be
                              attached to the invoice
       :return: dict of value to create() the invoice
    """
    if context is None:
        context = {}
    journal_ids = self.pool.get('account.journal').search(cr, uid,
        [('type', '=', 'sale'), ('company_id', '=', order.company_id.id)],
        limit=1)
    if not journal_ids:
        raise osv.except_osv(_('Error!'),
            _('Please define sales journal for this company: "%s" (id:%d).') % (order.company_id.name, order.company_id.id))
    invoice_vals = {
        'name': order.client_order_ref or '',
        'origin': order.name,
        'type': 'out_invoice',
        'reference': order.client_order_ref or order.name,
        'account_id': order.partner_invoice_id.property_account_receivable.id,
        'partner_id': order.partner_invoice_id.id,
        'journal_id': journal_ids[0],
        'invoice_line': [(6, 0, lines)],
        'currency_id': order.pricelist_id.currency_id.id,
        'comment': order.note,
        'payment_term': order.payment_term and order.payment_term.id or False,
        'fiscal_position': order.fiscal_position.id or order.partner_invoice_id.property_account_position.id,
        'date_invoice': context.get('date_invoice', False),
        'company_id': order.company_id.id,
        'user_id': order.user_id and order.user_id.id or False,
        'section_id' : order.section_id.id,
        'order_field':order.order
    }

    # Care for deprecated _inv_get() hook - FIXME: to be removed after 6.1
    invoice_vals.update(self._inv_get(cr, uid, order, context=context))
    return invoice_vals

      

        
        
        
      

    

I am overriding the method from sale.py 'order_field' - my field in account.invoice model.and the order is the same in sale.order.