Translation:Isn't it dirty?
きたない means dirty. きたなくない is its negative form (i.e. not dirty). い adjectives change to negative when い is replaced with くない.
I think what yagito meant was that the dots that help tell you a new word did not say that 「きたなくない」meant dirty. It gave other options such as: have/has, came; to be here and postage stamp even if you clicked different parts of it. That's what had happened to me at least.