Duplicate classification of material &1

What causes this issue?

No unique class assignment could be determined.

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

System Response

As SAP APO currently supports only simple classification for the CDP
(Characteristics Dependent Planning) classification system, no material
class will be transferred for this material.
If you have set the ERP classification system as the classification
system in SAP APO you can ignore this message.

How to fix this error?

Ensure that all classes used in the material master have the same name.
If necessary, change the names.

Error message extract from SAP system. Copyright SAP SE.