Not possible to plan this material since it is a planning material

What causes this issue?

The material in this plant is already being used as a planning material
in another material master record.
Since only single-level planning is possible, you cannot assign a
planning material.

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

System Response

How to fix this error?

Error message extract from SAP system. Copyright SAP SE.