Diagnosis
You wanted to perform a revaluation at retail that does not affectmargins. In this case, the purchase price and the cost value arechanged in the same ratio as the retail price and the retail value.
If you revaluate at retail not affecting margins on the basis of thedata you entered, the purchase price would be zero. This is notallowed.

Procedure
Check your entries. If your entries are correct, check the InventoryManagement and Valuation.