system Genrate Message when profit less than 20 % In Sales Quotation

Dear All

In Sales Quotation in have multiple line and my requirement is that when profit is less than 20 % per line (check every line),system genrate message and stop, untill profit greater than 20 %, i already check Approval Procedures, its work only for header and in row level ,check only first line

Using SAP B1 2007 A Sp 00 PL 47

Any Body tell me how we can genrate our message in system

Regards,

Haider