Error executing child request

[David C]

I am getting the following error on one of my aspx pages. The page where
the error is occurring is during a Page_Load on a page that was accessed via
a PostBackURL from a LinkButton on a previous page. Can anyone help?
Following the error is the part of my code where the error is occurring. It
is erroring on the line "If Not Page.PreviousPage Is Nothing Then". Thanks.
-David

Error executing child request for handler 'ASP.frmpropertyclosings_aspx'.

Stack Trace:
at System.Web.HttpServerUtility.ExecuteInternal(IHttpHandler handler,
TextWriter writer, Boolean preserveForm, Boolean setPreviousPage,
VirtualPath path, VirtualPath filePath, String physPath, Exception error,
String queryStringOverride)
at System.Web.HttpServerUtility.Execute(IHttpHandler handler, TextWriter
writer, Boolean preserveForm, Boolean setPreviousPage)
at System.Web.UI.Page.get_PreviousPage()
at frmListingDocs.Page_Load(Object sender, EventArgs e) in
http://server/rfpweboffice/frmListingDocs.aspx.vb:line 54
at System.Web.UI.Control.OnLoad(EventArgs e)
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
at System.Web.UI.Page.ProcessRequest(Boolean
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
at System.Web.UI.Page.ProcessRequest()
at System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context)
at System.Web.UI.Page.ProcessRequest(HttpContext context)
at ASP.frmlistingdocs_aspx.ProcessRequest(HttpContext context)
at
System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean&
completedSynchronously)


If Not Page.IsPostBack Then
'First page visit
If Not Page.PreviousPage Is Nothing Then
'Coming from frmProperty page
Dim strFolderPath As String = ""
Dim strFolderName As String = ""
Select Case strListType
Case "list"
SourceTextBox =
CType(PreviousPage.FindControl("txtAddressTop"), TextBox)
strFolderName =
UtilClass.ReplaceFolderChars(SourceTextBox.Text)
strFolderPath = VirtualListingRoot & strFolderName

Case "close"
SourceTextBox =
CType(PreviousPage.FindControl("txtClosingName"), TextBox)
strFolderName =
UtilClass.ReplaceFolderChars(SourceTextBox.Text)
strFolderPath = VirtualClosedRoot & strFolderName

Case Else 'expired
SourceTextBox =
CType(PreviousPage.FindControl("txtAddressTop"), TextBox)
strFolderName =
UtilClass.ReplaceFolderChars(SourceTextBox.Text)
strFolderPath = VirtualExpiredRoot & strFolderName
End Select
txtAddress.Text = strFolderName

......