Executing a VB WebMethod from javascript

I'm trying to eliminate a VB.NET button on my aspx page. Trying to use javascript and ajax to execute the same code my vb had.

I put in a script manager, set EnablePageMethods to true, added a static subroutine, and referred to it in my javascript function (BTW -- this seems a lot of work just to execute an existing subroutine). The javascript calls my code-behind and it almost works.

Problem is, now I'm getting a NullReferenceException when SimulatePrintBatchClick tries to do anything with the controls.

Error is 'Object reference not set to an instance of an object', line is 'pnlVars.Controls.Clear'

Here's the code from UW.aspx:

<WebMethod()> _
Public Shared Sub PrintBatchFromJSWM()
    Dim UWI As New UW

    UWI.SimulatePrintBatchClick()
End Sub


Sub SimulatePrintBatchClick()
    Dim Client As New LetterWriterClient

    'Run ExStream and get the PDF File
    Globals.PDF_Data = Nothing
    Globals.PDF_Data = Client.ProcessDatFile(Session("SessionID").ToString)

    'Reload the form -- turn off all controls, initialize variables and make the PDF iFrame visible
    pnlVars.Controls.Clear() 'Bombs out on THIS line of code
    pnlPDF.Visible = True
    Me.SendToBach.Visible = False
    Session.Contents("LetterVariables") = Nothing
    Session.Contents("PolicyInformation") = Nothing
    Session.Contents("Submitted") = True
    Response.Redirect("UW.aspx")
End Sub

Funny, when I run the above code in PrintBatch_Click it all executes just fine. I really don't understand why it bombs out as a subroutine.

Perhaps this is not the way to do this, but I'm at a loss for finding a different way. Originally this code was handled by an ASP/VB button, but the specs have called for it to be deleted.

Any way I can get the above code to do it's job?

Thanks, Jason