Diagnosis
You have created or changed a set. The set contains a value more thanonce, although the set definition specifies that this is not allowed.

System Response
The system does not allow you to create or change the set.

Procedure
Either correct the set so that it does not contain any value more thanonce, or change your settings so that a value can occur more than oncein the set (in other words, deselect the ambiguity check in the headerscreen for set maintenance).
If you cannot find the multiple occurrences of values in this set,first permit multiple occurrences of a value and save the set. You canthen carry out an ambiguity check (by choosing "Utilities -> Ambiguitycheck") which will show you the values that occur more than once,together with their path.