The valuation class cannot be changed, choose 'Display error'

What causes this issue?

You wanted to change the valuation class. However, this is not possible
because one or more of the following already exist for the material:
<DS:GLOS.3526C0B7AFAB52B9E10000009B38F974>Valuated stocks</> in the
current period or in the previous period
Open <DS:GLOS.3526C0CEAFAB52B9E10000009B38F974>purchase orders</> or
<DS:GLOS.3526C017AFAB52B9E10000009B38F974>delivery schedule lines</>
<DS:GLOS.3526C388AFAB52B9E10000009B38F974>Production orders</> for
which a goods movement has already taken place

System Response

Your change is reset by the system.

How to fix this error?

If valuated stocks already exist, you can change the valuation class
only as follows:
Post the stocks of the material to an interim account.
Change the valuation class in the material master record.
Post the stocks of the material back to their original account.
If open purchase orders already exist, you can only change the
valuation class if you first flag the corresponding purchase order
items for deletion.
If production orders exist for which a goods movement has already taken
place, you can only change the valuation class if you first set the
status of the production orders to <LS>Deleted</>.

Procedure for System Administrators

In Customizing for the <LS>Material Master</>, you can switch the check
for open purchase orders and/or for production orders to a warning. You
do this in <DS:SIMG.SIMG_CFMENUOLMSOMT4>Define Attributes of System
Messages</> by assigning the message type <LS>Warning</> to message MM
326 and/or MM 327 respectively. However, first ensure organizationally
that further processing of the open purchase orders or production
orders cannot result in inconsistencies.

Error message extract from SAP system. Copyright SAP SE.