Serial number requires reference row or a material number

What causes this issue?

For stock upload items of type <ZK>6</> (Serial Number), a material
number is required in case of serialization on warehouse level. For
serialization on stock level, the field REFROW has to contain the row of
the stock upload item of type <ZK>4</> (Material).

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

System Response

How to fix this error?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.