There are still production orders for the material

What causes this issue?

You wanted to change the valuation class. However, the material still
has production orders for which a goods movement has already taken
place. This can result in inconsistencies if the production orders are
processed further.
<ZH>Note</>
This message or the setting in Customizing for this message (see below)
is also relevant if the
<DS:GLOS.3526C022AFAB52B9E10000009B38F974>material type</> of a
material is changed and if the new material type requires another
valuation class to be assigned.

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?

Set the status of these production orders to deleted.

Procedure for System Administrators

In Customizing for the <LS>Material Master</>, you can define that this
message appears only as a warning. You do this in
<DS:SIMG.SIMG_CFMENUOLMSOMT4>Define Attributes of System Messages</>.
However, first ensure organizationally that further processing of the
production orders cannot result in inconsistencies.
Due to the importance of this message, it still appears as a warning
even if you assign the message type <LS>No message</> to it.

Error message extract from SAP system. Copyright SAP SE.