Stuck at Delivery processing => Picking & Post Goods

Hi, I am tyingto simulate a simple sales order workflow

1) I created a sales order with just one material

2) created delivery out of this sales order

3) Next step should be crate "Transfer Oder" and then "Post Goods Issue". When I press "Post Goods Issues" form delivery document this is the error I get

4) i also try to create "Transfer order" manually Logistics => Sales and Distribution => Shipping and Transportation => Picking => Create Transfer Order => LT03-Single Document

But here is asks me Warehouse Number (mandatory field!).

How can I proceed further to deliver t he goods & make billing.

- how do I remove the requirement to enter Warehouse Number?

- or, Whe re can I locate it from?

Is it so that "Picking" is being controlled via WM module (how can I de-activate it). I just want to simulate a simple sales order!

Thanks in advance for any relevant pointers.

best wishes,

/V