Linguistic labels are fuzzy sets (FuzzySet). Each label of the variable must have a unique name. The range of the label (left and right limits) cannot be greater than the linguistic variable range (start/end).
The fuzzy set was not initialized. The linguistic label name already exists in the linguistic variable. The left limit of the fuzzy set can not be lower than the linguistic variable's starting point. "The right limit of the fuzzy set can not be greater than the linguistic variable's ending point."