This function is not possible for split-valuated materials

What causes this issue?

A marked standard cost estimate exists for material &V2& in valuation
are &V1&. The material has separate valuation types. Standard cost
estimates for separately valuated materials cannot be released using
transaction MR21.

System Response

This function is not allowed in the system.

How to fix this error?

To release the standard cost estimate, use either transaction CK24 or
CKME.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.