Error executing child request

[David C]

We have a user getting an error message as follows:

Error executing child request for handler 'ASP.frmpropert yclosings_aspx' .

The line in the code-behind page that is causing the error is below.

If Not Page.PreviousPa ge Is Nothing Then

I cannot figure out why this error is occurring and wondered if anybody had
any ideas. Below is the stack trace. Thanks.
-David

Stack Trace:
at System.Web.Http ServerUtility.E xecuteInternal( IHttpHandler handler,
TextWriter writer, Boolean preserveForm, Boolean setPreviousPage ,
VirtualPath path, VirtualPath filePath, String physPath, Exception error,
String queryStringOver ride)
at System.Web.UI.P age.get_Previou sPage()
at frmListingDocs. Page_Load(Objec t sender, EventArgs e) in
http://server//RFPWebOffice/frmListingDocs.aspx.vb:line 54
at System.Web.UI.C ontrol.OnLoad(E ventArgs e)
at System.Web.UI.C ontrol.LoadRecu rsive()
at System.Web.UI.P age.ProcessRequ estMain(Boolean
includeStagesBe foreAsyncPoint, Boolean includeStagesAf terAsyncPoint)
at System.Web.UI.P age.ProcessRequ est(Boolean
includeStagesBe foreAsyncPoint, Boolean includeStagesAf terAsyncPoint)
at System.Web.UI.P age.ProcessRequ est()
at System.Web.UI.P age.ProcessRequ estWithNoAssert (HttpContext context)
at System.Web.UI.P age.ProcessRequ est(HttpContext context)
at ASP.frmlistingd ocs_aspx.Proces sRequest(HttpCo ntext context)
at
System.Web.Http Application.Cal lHandlerExecuti onStep.System.W eb.HttpApplicat ion.IExecutionS tep.Execute()
at System.Web.Http Application.Exe cuteStep(IExecu tionStep step, Boolean&
completedSynchr onously)