Intercompany sales order : OD with error " Enter Purchase Order "

Hi,

I am creating a intercompany sales order with movement type : 645. Now when i am performing the Goods Issue. it is giving a error

MSG          Area        Message type              Message Text

018            M7           E                                Enter Purchase Order

I have checked all the configuration regarding the movement type, screen layout. No where purchase order is maintained as mandatory.

Thanks in Advance

Regards

Ashish Philip