The data in the substance value assignment type &1 overlaps

What causes this issue?

The data in the substance value assignment type &V1& under rating &V2&
and validity area &V3& has not been entered correctly because there is
more than one value assignment instance for a usage. This message may
also have been triggered by an attempt to group the data for a number
of ratings in one inspection plan, and some of the data overlaps.

System Response

This data cannot be transferred to the inspection plan.

How to fix this error?

Check the data in the relevant substance value assignment type.

Error message extract from SAP system. Copyright SAP SE.