Visibility Expression regarding data value

Visibility Expression regarding data value

I have a table with 4 columns: AKA, Value, Unit, and Metric.
I have a filter on the dataset on AKA based on a parameter. I am trying to
use the following in the visibility filter:
=IIF(Fields!Metric.Value, "MONTHLY_SummaryStats" = "Availablility", FALSE,
TRUE)
I am getting an error regarding the expression referring directly to a
field without a dataset aggregate.
Any idea why it's asking for an aggregate when I am trying to filter on a
specific value?
Based on the filter on the dataset, this expression should only return 1
value.