Diagnosis
In Product Cost by Period,work in process can onlybe calculated at target cost. This is because thevariance calculationprocess only calculates variances by period, so WIP at actual costswould not be included. This would result in actual costs being settledmore than once.
You are using Product Cost by Period if there is a periodicdistribution rule in thesettlement rule thatsettles to material with a percentage of greater than 0.

Procedure
Use full settlement orcalculate the work in process at target costs.