Crystal Reports passing parameter to CR document

Message

   hi
i am getting a real troule with my code, i would like to pass a parameter to my crystal Repot document from my code(i am programming wi VB.NET VS2005)
my code in the following:

Dim cryRpt As New ReportDocument

cryRpt.Load("D:\imp_bon_reception.rpt", OpenReportMethod.OpenReportByDefault)

Dim crParameterFieldDefinitions As ParameterFieldDefinitions

Dim crParameterFieldDefinition As ParameterFieldDefinition

Dim crParameterValues As New ParameterValues

Dim crParameterDiscreteValue As New ParameterDiscreteValue

crParameterDiscreteValue.Value = Convert.ToInt32(bon_reception.TextB_num.Text)
crParameterFieldDefinitions = cryRpt.DataDefinition.ParameterFields
crParameterFieldDefinition = crParameterFieldDefinitions.Item("num_br")

crParameterValues = crParameterFieldDefinition.CurrentValues
crParameterValues.Clear()
crParameterValues.Add(crParameterDiscreteValue)
crParameterFieldDefinition.ApplyCurrentValues(crParameterValues)
CrystalReportViewer1.ReportSource = cryRpt
CrystalReportViewer1.Refresh()

but i got the fellowing error message in the bold line:

An unhandled exception of type 'System.Runtime.InteropServices.COMException' occurred in CrystalDecisions.CrystalReports.Engine.dll

Additional information: Index non valide. (Exception de HRESULT : 0x8002000B (DISP_E_BADINDEX)) 

 can you help me to solve this problem ?