Retrieving values using PreviousPage

I am new to asp.Net.  I am attempting to retrieve values from fields on a previous page assign their values to fields on the new page and insert those values into a table.  

When the page loads the previous page values do appear in the correct fields but I keep getting the following error: "Object reference not set to an instance of an object. " 

The line of code identified is: Line 133:    Dim myPage As ContentPlaceHolder = PreviousPage.Master.FindControl("ContentPlaceHolder1")

Here is my code:
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
 
        Dim body As HtmlGenericControl = Master.FindControl("MasterBody")
        body.Attributes.Add("onkeydown", "HandleRefresh(event,'" & Request.RawUrl & "');")
        Dim myPage As ContentPlaceHolder = PreviousPage.Master.FindControl("ContentPlaceHolder1")
 
        Dim EmpName As DropDownList = myPage.FindControl("EmpNameCom")
        EN = EmpName.SelectedValue
        Dim RevName As DropDownList = myPage.FindControl("RevNameCom")
        Rev = RevName.SelectedValue
        Dim EmpPos As DropDownList = myPage.FindControl("EmpPosCom")
        Pos = EmpPos.SelectedValue
        Dim State As DropDownList = myPage.FindControl("StateCom")
        St = State.SelectedValue
        Dim SurveyType As DropDownList = myPage.FindControl("SurveyTypeCom")
        SurT = SurveyType.SelectedValue
 
    End Sub
 
    Protected Sub Page_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreRender
        'sets the FormView in the correct mode depending on the action
        Dim myPage As ContentPlaceHolder = Page.Master.FindControl("ContentPlaceholder1")
        Dim fv As FormView = myPage.FindControl("FormView1")
        If Request.QueryString("mode") = "3" Then
            Me.FormView1.ChangeMode(FormViewMode.Edit)
            'If IsPostBack Then
            '    getClaimRepData()
            'End If
        ElseIf Request.QueryString("mode") = "1" Then
            Me.FormView1.ChangeMode(FormViewMode.ReadOnly)
        Else
            Me.FormView1.ChangeMode(FormViewMode.Insert)
            Dim txt As TextBox = fv.FindControl("SurveyDate")
            txt.Text = FormatDateTime(Now(), DateFormat.ShortDate)
            Dim txt1 As TextBox = fv.FindControl("EmpName")
            txt1.Text = EN
            Dim txt2 As TextBox = fv.FindControl("RevName")
            txt2.Text = Rev
            Dim txt3 As TextBox = fv.FindControl("EmpPos")
            txt3.Text = Pos
            Dim txt4 As DropDownList = fv.FindControl("State")
            txt4.SelectedValue = St
            Dim txt5 As TextBox = fv.FindControl("SurveyType")
            txt5.Text = SurT
        End If
 
    End Sub

Select allOpen in new window