Grazie della risposta
ho risolto così e non so il perchè 
codice:
Private Sub report_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
'TODO: This line of code loads data into the 'assegnazioniDataSet.ASSEGNAZIONI' table. You can move, or remove it, as needed.
Dim Params As List(Of Microsoft.Reporting.WinForms.ReportParameter) = _
New List(Of Microsoft.Reporting.WinForms.ReportParameter)
Params.Add(New Microsoft.Reporting.WinForms.ReportParameter("id", Val(s(0))))
ReportViewer1.LocalReport.SetParameters(Params)
Me.ASSEGNAZIONITableAdapter.FillBy(assegnazioniDataSet.ASSEGNAZIONI, s(0))
Me.ReportViewer1.RefreshReport()
End Sub