Getting error on RDLC parameter not defined in this report

[dbrewerton]

Does anyone know what causes this problem? I have a winforms report viewer and I have declared the variables on the report. There are three, StartDate, EndDate, and PatientID. Here is my code:

        public BPReport()
        {
            InitializeComponent();
            DateTime StartDate = DateTime.Today.AddDays(-30);
            DateTime EndDate = DateTime.Today.AddDays(0);
            BaseForm BForm = new BaseForm();
            string PatientID = BForm.PatientIDVal.ToString();
            reportViewer1.Clear();
            ReportParameter[] Param = new ReportParameter[3];
            Param[0] = new ReportParameter("StartDate", StartDate.ToString());
            Param[1] = new ReportParameter("EndDate", EndDate.ToString());
            Param[2] = new ReportParameter("PatientID", PatientID.ToString());
            this.reportViewer1.LocalReport.SetParameters(Param);
            this.reportViewer1.RefreshReport();
        }

Any ideas?