Parmeters problem in Report

I have created a report in Visual Basic 2005. Placed a Text Field. Added a parmeter to report paramA as string.
Set the value property of TextBox to Parameters!paramA.value.

Now from the The form(adding connection and dataset of course) where i have inserted a reportviewer I set the code for passing the parameter paramA 's value as :
//
Dim paramA as String ="TestValue"
Dim params(0) As ReportParameter
params(0) = New ReportParameter("paramA", paramA)
ReportViewer1.LocalReport.SetParameters(params) ReportViewer1.RefreshReport()
//
Now when I run the project the message says: "value can not be null"
Where I am Wrong?