Further material allocations exist. Deletion not possible

What causes this issue?

You can only delete material groups if both the following conditions
are fulfilled:

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

No materials (except the value-only material and reference material)
are assigned to the material group
The material group is not assigned to plants

System Response

How to fix this error?

Check the material assignments using the relevant function.

Error message extract from SAP system. Copyright SAP SE.