I am doing the basic drilldown that you learn in an intro to SSRS. No big deal, takes 30 seconds to set up and you should be on your way. My drilldown works fine when I preview in Visual Studio as well as on my report server website. But in my ASP.net application the report renders, I have the groups to start as collapsed. I click to expand a group and I get a failure. The same thing happens if I make the default for the groups to be expanded and click to collapse.
This report requires a default or user-defined value for the report parameter 'myParameter'. To run or subscribe to this report, you must provide a parameter value. (rsReportParameterValueNotSet)