--- sale.py.old	2011-07-01 13:25:12.748837652 +0200
+++ sale.py	2011-07-01 13:20:11.652846124 +0200
@@ -461,6 +461,8 @@
         res = False
         invoices = {}
         invoice_ids = []
+        #group the pricelist of different sales order for the same partner
+        partner_pricelist_group={}
         picking_obj = self.pool.get('stock.picking')
         invoice = self.pool.get('account.invoice')
         obj_sale_order_line = self.pool.get('sale.order.line')
@@ -477,6 +479,11 @@
                     continue
                 elif (line.state in states):
                     lines.append(line.id)
+            if o.partner_id.id  in partner_pricelist_group:
+                if o.pricelist_id.id not in partner_pricelist_group[o.partner_id.id]:
+                    partner_pricelist_group[o.partner_id.id].append(o.pricelist_id.id)
+            else:
+                partner_pricelist_group[o.partner_id.id]=[o.pricelist_id.id]
             created_lines = obj_sale_order_line.invoice_line_create(cr, uid, lines)
             if created_lines:
                 invoices.setdefault(o.partner_id.id, []).append((o, created_lines))
@@ -487,6 +494,10 @@
                         return i.id
         for val in invoices.values():
             if grouped:
+                if len([ s for s in partner_pricelist_group.values() if len(s)!=1]) !=0:
+                    raise osv.except_osv(_('Could not group these sales order in a same invoice!'),
+                                         _('You are trying to group sales order with different pricelist in a same invoice!'))
+
                 res = self._make_invoice(cr, uid, val[0][0], reduce(lambda x, y: x + y, [l for o, l in val], []), context=context)
                 invoice_ref = ''
                 for o, l in val: