service PO error-u201CPlease enter either material

Dear Friends ,

While making service PO following error coming.

u201CPlease enter either material or short text

Message no. MEPO052u201D

I have created service u2013AC01

Then ML33- for price record

Now doing PO selecting Acc Ass cat-K and Item category u2013D

At the time of saving doc. Systm give above error.

Regards,

Mahesh.