Report Designer - Conditional Count

Hello,

I'm working with Report Designer 1.0.

I have a table grouping where one field contains the following script (which is erroring at runtime):

=IIF(COUNT(IIF(Fields!PARTNERVALIDATIONSTATUS.Value=0, 1, Nothing))>0,"N/A",MAX(Fields!MODIFIEDDATETIME.Value))

I want to count the number of records in the result set that have a value of 0 in PARTNERVALIDATIONSTATUS.  If there is one or more, I would like to print "N/A" in that field.  If the result is 0 records, I would like to print the most recent date from the MODIFIEDDATETIME field.

Many thanks,

Jens