Char. &: sample unit & cannot be used with material &

What causes this issue?

The sample unit for the specified characteristic cannot be converted
into the material unit of measure. The characteristic would, however,
be used in an inspection of the material.

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?

Check the characteristic sample unit.

Error message extract from SAP system. Copyright SAP SE.