Unit conversion not possible from & to &

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

What causes this issue?

You are trying to convert unit of measure/currency unit &v1& to unit of
measure/currency unit &v2& . This was not successful. There are several
possible reasons:
There is no factor for this conversion in the product master
A product master does not exist for this product
No characteristic has been specified for the products
The currency settings are incorrect
Reset N1

System Response

How to fix this error?

Check that product masters exist for all the product in the current
selection
Check that conversion factors have been maintained between unit &v1&
and &v2& for each of these products
Check that characteristic 9AMATNR ihas been included in the master
palnning object structure or that another characteristic has been
assigned to the product.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.