Override default parameter with expression in linked report - not working

Hi there

I have a linked report with a parameter accepting a DateTime value. According to http://msdn.microsoft.com/en-us/library/ms189700.aspx I should be able to type an expression in here.

If Default Value accepts a value, you can type a constant or syntax that is valid for the data processing extension used with the report

I have "=DATEADD('d',-5,TODAY())" in the Default Value and am getting 

Josh Ash