Error adding new item line in Purchase Order

Hi all,
i inherited state in purchase.order - added Revision, Close.
the Revision state is to allow Purchase Order to revise the price or add item after approved.But what happend is i can't add new item line in this added state, it'll always prompt the below error msg.

Environment Information :
System : Windows-post2008Server-6.1.7600
OS Name : nt
Operating System Release : post2008Server
Operating System Version : 6.1.7600
Operating System Architecture : 32bit
Operating System Locale : en_US.cp1252
Python Version : 2.6.5
OpenERP-Client Version : 6.1.1
Last revision No. & ID :Bazaar Package not Found !Traceback (most recent call last):
  File "netsvc.pyo", line 489, in dispatch
  File "service\web_services.pyo", line 599, in dispatch
  File "osv\osv.pyo", line 122, in wrapper
  File "osv\osv.pyo", line 176, in execute
  File "osv\osv.pyo", line 167, in execute_cr
  File "osv\orm.pyo", line 2947, in read
  File "osv\orm.pyo", line 3070, in _read_flat
KeyError: 10340

after i researched i found out that it only happened to meet this error if we're adding a new item line beyond the state provided by the core.
i tried add in done & approve state, it allows me, but not in my revision or close state.
i wonder if there're any static rules or anything that prevent us from adding item line

Please help, i'm in urgentThx a lot in advance