I used this script when I added the dimension =Only({<[Condition of Car]={'Faulty'}>} [Status]) and the expression editor keeps showing it is okay. However, once I click okay I get an invalid dimension. When I used the alternative solution =Aggr(Only({<[Condition of Car]={'Faulty'}>} Status), Status) then I get duplicates in my data that I don't want.

Is there a reason the first script will keep throwing back an invalid dimension?

The expression
=Only({<[Condition of Car]={'Faulty'}>} [Status])
is a valid measure, but not a valid dimension.

Unfortunaltely, the expression editor thinks the syntax is OK, when it in fact isn't.

The expression
=Aggr(Only({<[Condition of Car]={'Faulty'}>} Status), Status)
is a a valid dimension.

Where do you get duplicates?