when i click the arow for drop down menue in employee field i recieve a long error log that ends with that line, i tried to look for that field and i couldnt find in which table or moduel it is. Can you please explain it for me (ValueError :....)

the module was running perfect but the moment i logged out and back in again it stopped working

Server Traceback (most recent call last):
  File "C:\Program Files (x86)\OpenERP 7.0-20140413-231155\Server\server\openerp\addons\web\session.py", line 89, in send
  File "C:\Program Files (x86)\OpenERP 7.0-20140413-231155\Server\server\.\openerp\netsvc.py", line 296, in dispatch_rpc
  File "C:\Program Files (x86)\OpenERP 7.0-20140413-231155\Server\server\.\openerp\service\web_services.py", line 626, in dispatch
  File "C:\Program Files (x86)\OpenERP 7.0-20140413-231155\Server\server\.\openerp\osv\osv.py", line 190, in execute_kw
  File "C:\Program Files (x86)\OpenERP 7.0-20140413-231155\Server\server\.\openerp\osv\osv.py", line 132, in wrapper
  File "C:\Program Files (x86)\OpenERP 7.0-20140413-231155\Server\server\.\openerp\osv\osv.py", line 199, in execute
  File "C:\Program Files (x86)\OpenERP 7.0-20140413-231155\Server\server\openerp\addons\audittrail\audittrail.py", line 532, in execute_cr
  File "C:\Program Files (x86)\OpenERP 7.0-20140413-231155\Server\server\.\openerp\osv\osv.py", line 187, in execute_cr
  File "C:\Program Files (x86)\OpenERP 7.0-20140413-231155\Server\server\.\openerp\osv\orm.py", line 2415, in name_search
  File "C:\Program Files (x86)\OpenERP 7.0-20140413-231155\Server\server\.\openerp\osv\orm.py", line 2446, in _name_search
  File "C:\Program Files (x86)\OpenERP 7.0-20140413-231155\Server\server\.\openerp\osv\orm.py", line 4931, in _search
  File "C:\Program Files (x86)\OpenERP 7.0-20140413-231155\Server\server\.\openerp\osv\orm.py", line 4757, in _where_calc
  File "C:\Program Files (x86)\OpenERP 7.0-20140413-231155\Server\server\.\openerp\osv\expression.py", line 646, in __init__
  File "C:\Program Files (x86)\OpenERP 7.0-20140413-231155\Server\server\.\openerp\osv\expression.py", line 810, in parse

ValueError: Invalid field u'hr_employee' in leaf "<osv.ExtendedLeaf: (u'hr_employee', u'=', False) on hr_employee (ctx: )>"