Diagnosis
When you assign a nutrient to a characteristic, the unit of thecharacteristic and the unit of the nutrient have to belong to the samedimension.
Example:
Unit of characteristic = mg, unit of nutrient = g ->permitted, since bothunits belong to the Mass dimension.
Unit of characteristic = ml, unit of nutrient = g -> not permitted,since the units belong to different dimensions.

Procedure
Check the unit of the characteristic and of the nutrient and adjust themif necessary.