ASP.Net ArrayList count Error: Object reference not set to an instance of an object

My asp.net/vb.net application has a code-behind file, PlanWizard.aspx.vb, that declares an ArrayList in the opening lines before any procedures as follow

Imports System.Data
Imports System.Data.SqlClient
Imports DAL

Partial Class WizardTest
    Inherits System.Web.UI.Page

    Private aryTaskWizarded As ArrayList

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Not Me.IsPostBack Then

            Me.hidWizTaskID.Value = Request.QueryString("TaskID")
            ...
            ...
            ...

            'Selected task will be the first item in array of tasks
            aryTaskWizarded = New ArrayList()
            aryTaskWizarded.Add(Me.hidWizTaskID.Value & "|" & Session("wizMainTaskName"))

            'Populate aryTaskWizarded with all members of 'me.hidWizTaskID.value's branch where ListComplete is false
            Sql = "execute uspBranchNotListComplete " & Me.hidWizTaskID.Value.ToString
            Dim dr As SqlDataReader = SqlHelper.ExecuteReader(Sql)
            While dr.Read
                aryTaskWizarded.Add(dr("TaskID") & "|" & dr("TaskName"))
            End While
            dr.Close()
            dr = Nothing
            ...
            ...
            ...
        End If
    End Sub
End Class

The Page_Load routine "sees" the aryTaskWizarded and runs as expected. The routine that runs when the Next button is clicked, however, crashes at a reference to the aryTaskWizarded variable. Here is that routine:

Protected Sub wizPP_NextButtonClick(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.WizardNavigationEventArgs) Handles wizPP.NextButtonClick
Dim sql As String = ""
Dim n As Integer = 0

Select Case wizPP.ActiveStepIndex
    Case 1 'wizPP_OneDay
        'Which radio button did user select?
        Select Case CType(wizPP_OneDay.FindControl("rdoYesNoSkip"), RadioButtonList).SelectedValue.ToString
            Case "Yes"
                ...
                ...
                ...
            Case "No"
                ...
                ...
                ...
            Case "Skip"
                'Move this task to the end of the list
                If (aryTaskWizarded.Count > 0) Then
                    'Copy current item on list
                    Dim TW As String = aryTaskWizarded(0)
                    'Delete from list
                    aryTaskWizarded.RemoveAt(0)
                    'If there's nothing left on the list, go to Finish
                    If aryTaskWizarded.Count = 0 Then
                        wizPP.ActiveStepIndex = 2
                    Else
                        'Add TW to the end of the list
                        aryTaskWizarded.Add(TW)
                    End If

                End If
                ...

The program crashes when it encounters the line "If (aryTaskWizarded.Count > 0) then" and displays the message, "Object reference not set to an instance of an object."

The facts that this occurs within an asp.net Wizard control may be relevant. Can anyone tell me what I am doing wrong, and how I can make the aryTaskWizarded variable accessible to the wizPP_NextButtonClick event handler and other procedures within the module? Thanks for any help.