SAP Message C4023 - & does not allow another unit

Diagnosis
The unit of measure for the characteristic cannot be converted into theunit of measure you entered. The unit of measure for the characteristicand the unit of measure you entered cannot be converted into otherunits of measure. Settings in the IMG determine whether alternativeunits can be entered.

Procedure
Enter the unit of measure defined in characteristics maintenance forthe characteristic, or enter a unit that can be converted into the unitfor the characteristic.