sub-contact problem

dear eperts,

i have created one material A as semi finished material,

i would like to get it from a sub contarcting vendor,

for that i created two raw materials B and C,

B and C are existed in my plant

i rated bom for A with B and C also

when i tried to make a sub contacting po to the vendor,

that gives the error : material can not determine any comonents

i have cretaed infor record ( sub-contarcting ) also,

when i created BOM ,it has given BOM is created for material A also

at the time po component or BOM switch is not appear at the line item for A,

how this is rectified,

reward points

regards