SAP Message BK042 - Unit of measure & cannot be converted to &

Diagnosis
You entered a unit of measure which is not normally used to record theconsumption, activity, or output in the cost center or order. This unitof measure is &V2&, not &V1&.
You can enter the quantity in another unit of measure, but this must beconvertible to &V2&. The given unit of measure &V1& cannot be convertedto &V2&.

Procedure
Do not enter a unit of measure. The system will then automaticallydefault to &V2&.
Alternatively, enter a unit of measure which can be converted to &V2&.