stock transfer purchase order

Hi expert

I have made 2 material having exactly same data. the difference between these 2 materials is material name, Material type and valuation class.

Material1 :- Material Type : Finished type (FERT), Valuation class : 3000

Material2 :- Material Type : Semifinished (HALB) ,Valuation class : 3100

THE PROBLEM IS for material1 i m able to make STPO .

but for material2 i m not able to make STPO. the error is shipping data is not available for MATERIAL2.

Can anyone plz tell me what can be possible error.