Material &1 has already been assigned. Please enter a new FFF class

What causes this issue?

Material &V1& has already been assigned to an
<DS:GLOS.3607AFB8AECD4ABAE10000009B38F9B8>FFF class</> for
inventory-managed manufacturer parts.

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?

Check, and if necessary correct, the entry.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.