variant in requisition worksheet

Hi To All memebers Plz sort out the problem as soon as possible How to calculate plan in requsition worksheet when Item is attached with varints.It is giving proper calculation when we are calculating for the first time.when we to try calculate plan again after posting it to create the Purchase Order using Function–>Carry Out Action Message it is showing wrong values. Waiting for early reply. thanks & Regrds aniruddha