Exception message 20

Dear All ,

we are working on strategy 40 . i have sales order of 10 Qty & in material master we have lot size procedure EX and the min lot size = 20 .

( as this part can be manufactured by us minimum 20 qty ) . By this the system is creating planned order with 20 qty .

Now this is with exception message 20 . But this is genuine , how to react or avoid this exception message ?>

Pl guide