Changing maxJsonLength property in web.config has no effect

I am using an MS Virtual Earth AJAX control to plot custom boundaries on amap in my ASP.Net 3.5 site.  I have a WCF service which I call from ASP.Net to return the points I need to plot.  In one instance, I need to plot ~40,000 points.  

I get the following error any time the amount of points (rows returned from WCF service) I need to plot are over 25,000.

Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property.

I tried modifying the maxJsonLength property in my web.config to 2147483647 but changing this value has no effect.  No matter what I set the value to, I always get an error when I try to plot more than 25,000 points.  I even tried setting it to "ABC" and my site still worked when my WCF service returned less than 25,000 records.  

I verified that I don't have the maxJsonLength property in my machine.config file.

Below is an excerpt from my web.config file:

<configuration>
      <configSections>
            <sectionGroup name="system.web.extensions" type="System.Web.Configuration.SystemWebExtensionsSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
                  <sectionGroup name="scripting" type="System.Web.Configuration.ScriptingSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
                        <section name="scriptResourceHandler" type="System.Web.Configuration.ScriptingScriptResourceHandlerSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/>
                        <sectionGroup name="webServices" type="System.Web.Configuration.ScriptingWebServicesSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
                              <section name="jsonSerialization" type="System.Web.Configuration.ScriptingJsonSerializationSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="Everywhere"/>
                              <section name="profileService" type="System.Web.Configuration.ScriptingProfileServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/>
                              <section name="authenticationService" type="System.Web.Configuration.ScriptingAuthenticationServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/>
                              <section name="roleService" type="System.Web.Configuration.ScriptingRoleServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" allowDefinition="MachineToApplication"/></sectionGroup></sectionGroup></sectionGroup></configSections><appSettings/>
      <connectionStrings/>
      <system.web.extensions>
            <scripting>
                  <webServices>
                        <jsonSerialization maxJsonLength="2147483647"/>
                  </webServices>
            </scripting>
      </system.web.extensions>

Any idea my changes to the maxJsonLength property aren't being recognized?