Compare Date Parameters on Report Viewer

Visual Studio 2010 (VB.NET)

Crystal Reports 2010

I have two date parameters in my report viewer (Start and End dates). When the user clicks the "Apply" button in the parameter panel is there any way to display a dialog box if the Start date is after the End date?

I don't see any event for the "Apply" button, just the "Refresh" button (the ReportRefresh event).