Group Filter Not Working

I'm developing a simple client application, using local reports populated from a local dataset, which is in turn saved and read from xml.
I am trying to set up a VERY simple group filter expression and I'm running into problems. What I want to do is display all rows where a date column matches a parameter passed to the report. I'm setting the filter up using something like this:
Expression Operator Value
=Fields!SampleDate = =Parameters!DateParam
I keep getting the following error:

Processing Errors
Value cannot be null.
Parameter name: value
OK

I know I'm probably doing something wrong. The only filter that I could get to not give the error is 1=1. LOL. Please help!You may want to try this approach:

Filter expression:
=(Fields!SampleDate.Value = Parameters!DateParam.Value)

Operator:
=

Filter Value:
=True
-- Robert