"Error: Sys.Net.WebServiceFailedException: The server method failed with the following error: -- There was an error processing the request."

I have a asp.net web application in which a JavaScript call is made to a web service which is written in VB.  The web service accesses a data set which is in a session variable and returns it as XML.  For most users the returned XML is a few thousand characters but for some it can be over 800,000.  The error in the title occurs when the XML is somewhere over 55,000 characters.  The error occurs in the depths of the auto generated JavaScript so I haven't had much luck debugging it however it is apparent that there is a default limit on the size of the string returned by web services.  I searched the web and found some things about disabling SOAP and setting the JSON size limit in web.config but that didn't work for me.  The code for the JavaScript and the web service are below.  Any suggestions would be greatly appreciated.

function PopulateRecordsFor() 
{
    try
    {
    RecordsForService.PopulateList(PopulateRecordsForCallBack);
    }
    catch (e) 
    {
        alert("Alert 1" + e.description);
    }
}

function PopulateRecordsForCallBack(result)
{
    try {
        var xmlDoc = new ActiveXObject("Microsoft.XMLDOM");
        xmlDoc.async = "false";
        xmlDoc.loadXML(result);
        var xmlname, xmlid
        var findNodes1 = xmlDoc.getElementsByTagName("Name");
        var ddl = $get("ctl00_ddlRecordsFor");
        for (i = 0; i < findNodes1.length; i++) {
            xmlname = xmlDoc.getElementsByTagName("Name")[i].childNodes[0].nodeValue;
            xmlid = xmlDoc.getElementsByTagName("FileNumber")[i].childNodes[0].nodeValue;
            var objOption = document.createElement("option");
            objOption.value = xmlid;
            objOption.text = xmlname;
            ddl.add(objOption);
        }
    }
    catch (e) 
    {
        alert("Alert 2" + e.description);
    }
}

Imports System.Web
Imports System.Web.Services
Imports System.Web.Services.Protocols
Imports System.Data
Imports System.Collections.Generic

<System.Web.Script.Services.ScriptService()> _
<WebService(Namespace:="http://People-Inc.org/")> _
<WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Public Class RecordsForService
    Inherits System.Web.Services.WebService

    <WebMethod(EnableSession:=True)> _
    Public Function PopulateList() As String
        Try
            Dim ds As DataSet = Session("CurrentUser").Individuals
            Return ds.GetXml()
        Catch ex As Exception
            Return "The following error has occurred on the Core Information form while attempting to populate the Records For list.' " _
             & ex.Message & "' Copy and paste this message into an e-mail to the IT help " _
             & "desk or call the IT help desk and read this exact message to them."
        End Try
    End Function

End Class

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