SAP Message XU046 - Unit of measure & is not a principal unit of measure. Please check.

Diagnosis
Processing is carried out for the material using proportion/productunits. Therefore, you can only use the principal alternative unit ofmeasure here.
In the case of proportion units, this unit of measure is explicitlydefined in the material master.
In the case of product units, this is the production unit. Theproduction unit must also be a product unit.

Procedure
Please choose another unit of measure.