PROBLEM IN SERVICE ENTRY SHEET

Dear cons

When we create a service purchase order the system automatically takes NO LIMITS. You can check it in item details of delivery tabs. Suppose we entered service of 15 EA in ser. P.o of service tabs. we create service entry sheet (ML81N) by adopting full quantity of p.o by service selection & after that selcting the item Then choose the service.at the time of choosing the service we want to enter the service of 16 EA. Because tolerance is marked NO LIMITS. But the system gives a message quantity exceeds from the p.o quantity. Pl. solve it. What is the meaning of NO limits.PL. SOLVE IT