I'm hoping someone can help me with a Cross Page Post Back

In the source page, I have declared a Public Property:

    Public ReadOnly Property userAccountID() As Int32
        Get
            Return registrationAccountID
        End Get
    End Property

In the Destination Page, I have declared a PreviousPage.

<%@ PreviousPageType VirtualPath="~/secure_members/accountDetails.aspx" %>

I am attempting to set the value of a control on a DetailsView control, inserting

    Protected Sub DetailsView1_ItemInserting(ByVal sender As Object, _
       ByVal e As System.Web.UI.WebControls.DetailsViewInsertEventAr gs) _
       Handles DetailsView1.ItemInserting
        e.Values("UserName") = User.Identity.Name
        e.Values("registrationEventID") = "1"
        e.Values("registrationAccountID") = PreviousPage.userAccountID
    End Sub

When I run the page, I get this error:

Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

Line 14: e.Values("registrationAccountID") = PreviousPage.userAccountID


What am I missing? When i typed the inserting object for the Account ID (e.Values("registrationAccountID") = PreviousPage.userAccountID), the userAccountID popped up in the intellisense so I thought it would work.

Any help is appreciated!