Diagnosis
If the characteristic is already assigned to a material group hierarchylevel, a material group, or a characteristic profile, the characteristicwith the current characteristic type may be used in operativeapplications, which means changing the characterstic type could resultin inconsistent data.
For this reason, you cannot change the characteristic type if one ormore assignments exist.

Procedure
Try to delete all existing assignments of the characteristic. If this ispossible, the characteristic is not used by any materials. You canchange the characteristic type. Then assign the characteristic again.