What causes this issue?

Valuation is at plant level. However, inconsistencies have arisen
because of the way in which the plant was configured in Customizing
or because plants have not been assigned to a company code.

System Response

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

How to fix this error?

INCLUDE NA_SYSTVERW1


Procedure for systems administrators
Check the assignment of plants to company code.
<DS:TRAN.OX18>Proceed</>
Check the configuration of the valuation level.
<DS:TRAN.OX14>Proceed</>
If the assignments are correct, check the entries in table T001W.
<DS:TRAN.SM31>Proceed</>

Error message extract from SAP system. Copyright SAP SE.