Material & is a material group reference material

What causes this issue?

You wanted to perform a function using a material with the material
category "material group reference material". However, this function is
not allowed for material group reference materials.

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?

Please check your entry.

Error message extract from SAP system. Copyright SAP SE.