I get an error when I am using IE7/IE8 (firefox works fine) when I create a new GWT module which uses the ApplicationRequestFactory

I have done the following
1. created a Roo project from the shell (much like expenses.roo in roo/samples)
2. imported the project into STS
3. created a new gwt module which calls the backend (using the ApplicationRequestFactory). The module inherits from ApplicationCommon. When I call the backend I get the error listed below.

I have tried coping the code from the scaffold class, but I still get an error in IE7/IE8 (not in firefox)

Any help?, what I am doing wrong?

Versions:
Roo: 1.1.0M3
Java: 1.6.0_20
STS: Version: 2.5.0.M3

Stacktrace:

com.google.gwt.core.client.JavaScriptException: (TypeError): '$wnd.JSON' is null or not an object
number: -2146823281
description: '$wnd.JSON' is null or not an object
at com.google.gwt.dev.shell.BrowserChannelServer.invo keJavascript(BrowserChannelServer.java:237)
at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke (ModuleSpaceOOPHM.java:126)
at com.google.gwt.dev.shell.ModuleSpace.invokeNative( ModuleSpace.java:552)
at com.google.gwt.dev.shell.ModuleSpace.invokeNativeO bject(ModuleSpace.java:269)
at com.google.gwt.dev.shell.JavaScriptHost.invokeNati veObject(JavaScriptHost.java:91)
at com.google.gwt.requestfactory.client.impl.ClientRe questHelper$MyJSO$.toJsonString$(ClientRequestHelp er.java)
at com.google.gwt.requestfactory.client.impl.ClientRe questHelper$MyJSO$.access$1(ClientRequestHelper.ja va:49)
at com.google.gwt.requestfactory.client.impl.ClientRe questHelper.getRequestString(ClientRequestHelper.j ava:63)
at com.google.gwt.requestfactory.client.impl.RequestF actoryJsonImpl.fire(RequestFactoryJsonImpl.java:84 )
at com.google.gwt.requestfactory.client.impl.Abstract Request.fire(AbstractRequest.java:76)
at com.ibm.gwt.client.Eplaster.onModuleLoad(Eplaster. java:39)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Nativ e Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknow n Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Un known Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.google.gwt.dev.shell.ModuleSpace.onLoad(Module Space.java:397)
at com.google.gwt.dev.shell.OophmSessionHandler.loadM odule(OophmSessionHandler.java:183)
at com.google.gwt.dev.shell.BrowserChannelServer.proc essConnection(BrowserChannelServer.java:510)
at com.google.gwt.dev.shell.BrowserChannelServer.run( BrowserChannelServer.java:352)
at java.lang.Thread.run(Unknown Source)