I'm currently using ASPXtoPDF (v 2011.2) to do a snapshot capture of a web form when the Submit button is clicked on the form, and it seems to work all the time in the VS 2010 (.Net 4 target) debugger environment and intermittently when used on a production web server.

Protected Sub ASPxButtonUpdate_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles ASPxButtonUpdate.Click
Try

Session("isRefStatSaveAttachDB") = True
ASPXToPDF1.RenderAsPDF(False)
Response.Redirect(DestinationPage, False)
Catch ex As System.Exception
sbErrMsgbuf.AppendLine(String.Format("{0}{1} ASPxButtonUpdate_Click {2}", SiteGlobals.sErrorPrefix, Me.Title, ex.Message))
End Try
End Sub

Protected Sub ASPXToPDF1_AfterRender(sender As Object, e As EventArgs) Handles ASPXToPDF1.AfterRender
Try
If Session("isRefStatSaveAttachDB") = True Then
'Cast the Result property to HtmlToPdfResult
Dim result As HtmlToPdfResult = CType(ASPXToPDF1.Result, HtmlToPdfResult)
If result Is Nothing Then
sbErrMsgbuf.AppendLine(String.Format("{0}{1} No Result from ASPXToPDF1_AfterRender", SiteGlobals.sErrorPrefix, Me.Title))
Else
'Get the result document
Dim doc As PdfDocument = result.PdfDocument
Dim ms As IO.MemoryStream = New IO.MemoryStream
result.PdfDocument.Save(ms)
Dim bPDFBytes As Byte() = ms.ToArray
Dim sPDFFileName As String = String.Format("PARForm_{0}_{1}.pdf", sEpiID, Session("VisCheck").ToString)
sbErrMsgbuf.AppendLine(SiteGlobals.Insert_AttachmenttoDBTable(bPDFBytes, sPDFFileName, sEpiID, Session("NonAspUserName"), ConfigurationManager.ConnectionStrings("cciddata").ConnectionString))
End If
End If

Catch ex As System.Exception
sbErrMsgbuf.AppendLine(String.Format("{0}{1} ASPXToPDF1_AfterRender {2}", SiteGlobals.sErrorPrefix, Me.Title, ex.Message))
End Try
End Sub 'ASPXToPDF1_AfterRender

This is the error I get intermittently:

Global_asax Application_Error Value cannot be null.
Parameter name: type
at System.Activator.CreateInstance(Type type, Boolean nonPublic)
at EO.Web.ASPXToPDF.a(String A_0, Stream A_1)
at EO.Web.Internal.mi.a(b[] A_0)
at System.Web.HttpWriter.FilterIntegrated(Boolean finalFiltering, IIS7WorkerRequest wr)
at System.Web.HttpResponse.FilterOutput()
at System.Web.HttpApplication.CallFilterExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Any ideas on possible solution?