using crystal reports with parameters

[DLT]

I have written a VB.NET application that contains several
crystal reports. I have created the reports with
parameters and am passing them fine into the report the
first time. But, if I change the values of the parameters
and try to generate the reports again, I am getting
prompted by Crystal reports to enter the discrete values.
Here's part of my code... It is executed when the user
selects the report and clicks a button. I don't understand
why I don't get prompted the first time, but do all
subsequent times:

Dim pField As New ParameterField()
Dim pParms As New ParameterFields()
Dim discreteVal As New ParameterDiscreteValue()

pField.ParameterFieldName = "beginDate"
discreteVal.Value = Convert_PC_Date(txtBeginDate.Text)
pField.CurrentValues.Add(discreteVal)
pParms.Add(pField)

pField = New ParameterField()
discreteVal = New ParameterDiscreteValue()
pField.ParameterFieldName = "endDate"
discreteVal.Value = Convert_PC_Date(txtEndDate.Text)
pField.CurrentValues.Add(discreteVal)

pParms.Add(pField)
crViewer.ParameterFieldInfo = pParms
crViewer.ReportSource = New BalanceYTD()