Hi,
well, I missed that the second question is an array(text).
Then you have to add the x_axis code as well.
And the validation is something like
questionOne_SQ003.NAOK!

OR (questionOne_SQ003.NAOK=

and !is_empty(questionTwo_SQ003_SQ001)).
And your mistake was:
Of course you have to adapt the validation, if you use different answer option codes instead my "1", "2", "3", but "A1", "A2",...
So the final should be
questionOne_SQ003.NAOK!="A3" OR (questionOne_SQ003.NAOK=="A3" and !is_empty(questionTwo_SQ003_SQ001))
Joffm