How to write visibility expression on two data fields?

I am developing an RDL on SSRS 2008 R2 and am trying to make one group display or hidden based on the following visiblity expression for this group:

=iif(ISNOTHING(Fields!test_setup_details_caption.Value)=1,
iif(Fields!test_setup_answers_value.Value=0,true,false),
false)

And the filter is set as this screenshot:

However, this group is still displaying even though test_setup_details_caption = 0 for "Self Suicidal" in the dataset.  I tried changing visibility logic to

=iif(ISNOTHING(Fields!test_setup_details_caption.Value)=1 and
Fields!test_setup_answers_value.Value=0,true,false)

but this resulted in an error.  What else can I try to get this group to show correctly?  I only want non-zero test_setup_details_caption rows and where test_setup_details_caption is not null to appear.

Ryan D