I have been trying to validate an invoice and have been getting the following error message. I have no technical knowledge, & have no idea how to solve it. Please help.

OpenERP Server Error Client Traceback (most recent call last): File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server\openerp\addons\web\http.py", line 204, in dispatch File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server\openerp\addons\web\controllers\main.py", line 1140, in exec_workflow File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server\openerp\addons\web\session.py", line 148, in exec_workflow File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server\openerp\addons\web\session.py", line 31, in proxy_method File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server\openerp\addons\web\session.py", line 104, in send

Server Traceback (most recent call last): File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server\openerp\addons\web\session.py", line 90, in send File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\netsvc.py", line 293, in dispatch_rpc File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\service\web_services.py", line 626, in dispatch File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\osv\osv.py", line 131, in wrapper File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\osv\osv.py", line 220, in exec_workflow File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\osv\osv.py", line 213, in exec_workflow_cr File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\osv\orm.py", line 3926, in _workflow_signal File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\workflow\wkf_service.py", line 119, in trg_validate File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\workflow\instance.py", line 43, in validate File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\workflow\workitem.py", line 60, in process File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\workflow\workitem.py", line 175, in _split_test File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\workflow\workitem.py", line 183, in _join_test File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\workflow\workitem.py", line 40, in create File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\workflow\workitem.py", line 52, in process File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\workflow\workitem.py", line 106, in _execute File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\workflow\wkf_expr.py", line 67, in execute File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\workflow\wkf_expr.py", line 57, in _eval_expr File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\tools\safe_eval.py", line 241, in safe_eval File "", line 1, in <module> File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server.\openerp\osv\orm.py", line 374, in function_proxy File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server\openerp\addons\account\account_invoice.py", line 1003, in action_move_create File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server\openerp\addons\account\account.py", line 1321, in post File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server\openerp\addons\base\ir\ir_sequence.py", line 222, in next_by_id File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server\openerp\addons\account\ir_sequence.py", line 57, in _next File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server\openerp\addons\base\ir\ir_sequence.py", line 213, in _next File "C:\Program Files\OpenERP 7.0-20130506-231027\Server\server\openerp\addons\base\ir\ir_sequence.py", line 176, in _interpolate TypeError: not enough arguments for format string