Cross company stock movements

Hi,

My client is wanting to do stock transfer from one company code to other.

But they want it to be done without PO from receiving company code.

I did same setting as required for Cross Company STO.

The want process as below,

SO (@ supplying plant)--->Delivery--->Billing

Once delivery is done stock have to up @ receving plant.

So i Created an order type ZTS1 copying OR

I created Item category ZTA1 copying TAN

Also assigned the delivery type LF

I created a Schedule line category by copying NC as ZC for movement type field entered 645,with item relevant for delivery field checked

Item category determination

ZTS1+NORM+-+-=ZTA1

Schedule line category determination.

ZTA1+-=ZC

After doing settings,

I have created order(maintained purchase order field)

With reference to order  ,i did delivery,once i clicked PGI.

System throws message

Enter Purchase Order

Message no. M7018

My doubt is,is that movement type 645 is hard coded in such a way PO field is must.

Thanks,

Pradeep