No measurement unit is assigned to ISO code &

What causes this issue?

No assignment to an internal code was found for ISO code &v1& for
measurement units. Either no such internal code exists,
or the internal code is not assigned to the ISO code.

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 assign an internal code to the ISO code.

Error message extract from SAP system. Copyright SAP SE.