Exploded structured material is ambiguous

What causes this issue?

Stock determination caused an error because the exploded structured
material is ambiguous.
The system can only update structured materials when the stock has been
determined uniquely.

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?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.