Quantity could not be converted from &1 to &2

What causes this issue?

You have tried to carry out a quantity conversion from &V1& to &V2& for
weight determination, because a different sales unit is defined for the
gross weight in the material master record.
This was not possible.

System Response

The system uses the net weight 0 for calculation.

How to fix this error?

Maintain the conversion factors of the weight units in the system.

Error message extract from SAP system. Copyright SAP SE.