Data Grid With Para Meter Question

I have the following code:
 Imports System
Imports System.Data.SqlClient

Namespace TestWeb


Partial Class araging

Inherits System.Web.UI.Page

Private _dt As DataTable
Private _connstr As String

#Region " Web Form Designer Generated Code "

'This call is required by the Web Form Designer.
<System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()

End Sub


Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
'CODEGEN: This method call is required by the Web Form Designer
'Do not modify it using the code editor.
InitializeComponent()
End Sub

#End Region

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

Dim _connstr As New SqlConnection(ConfigurationManager.ConnectionStrings("ESQLConn").ConnectionString)

Dim sqlCommand As SqlCommand = New SqlCommand("csp_rpt_ack_form", _connstr)


sqlCommand.CommandType = CommandType.StoredProcedure

Dim objaDapter As New SqlDataAdapter(sqlCommand)

objaDapter.SelectCommand.Parameters("@v_order_doc_no").Value = 272

Dim ds As New DataSet
objaDapter.Fill(ds)
mainGrid.DataSource = ds
mainGrid.DataBind()


Response.Write(_connstr)


End Sub



End Class


End Namespace

  
I am trying to pass a value to the parameter that it contains. What Im I doing wrong? I keep on getting the following message.
"
An SqlParameter with ParameterName '@v_order_doc_no' is not contained by this SqlParameterCollection."
 Thanks guys!