I am trying to claim to mass return by product lot number. I am getting the following error. Please help me.

Client Traceback (most recent call last): File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server\openerp\addons\web\common\http.py", line 180, in dispatch File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server\openerp\addons\web\controllers\main.py", line 1052, in call_button File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server\openerp\addons\web\controllers\main.py", line 996, in call_common File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server\openerp\addons\web\controllers\main.py", line 1010, in _call_kw File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server\openerp\addons\web\common\openerplib\main.py", line 250, in proxy File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server\openerp\addons\web\common\openerplib\main.py", line 117, in proxy File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server\openerp\addons\web\common\http.py", line 608, in send

Server Traceback (most recent call last): File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server\openerp\addons\web\common\http.py", line 593, in send File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server.\openerp\netsvc.py", line 360, in dispatch_rpc File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server.\openerp\service\web_services.py", line 586, in dispatch File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server.\openerp\osv\osv.py", line 167, in execute_kw File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server.\openerp\osv\osv.py", line 121, in wrapper File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server.\openerp\osv\osv.py", line 176, in execute File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server.\openerp\osv\osv.py", line 164, in execute_cr File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server\openerp\addons\crm_claim_rma\wizard\returned_lines_from_serial.py", line 107, in action_add_and_close File "C:\Program Files\OpenERP 6.1-20121130-002722\Server\server\openerp\addons\crm_claim_rma\wizard\returned_lines_from_serial.py", line 136, in add_return_lines AttributeError: 'NoneType' object has no attribute 'create'