I am getting the following error when retrieving data from a rest data source

00:00:52.439 [ERROR] 01:46:57.001:RDQ1:WARN:ResultSet:isc_ResultSet_1 (created by: isc_CustomerDocGrid_0):get: invalid index -1 com.smartgwt.client.core.JsObject$SGWT_WARN: 01:46:57.001:RDQ1:WARN:ResultSet:isc_ResultSet_1 (created by: isc_CustomerDocGrid_0):get: invalid index -1 at sun.reflect.NativeConstructorAccessorImpl.newInsta nce0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInsta nce(NativeConstructorAccessorImpl.java:39) at sun.reflect.DelegatingConstructorAccessorImpl.newI nstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Construc tor.java:513) at com.google.gwt.dev.shell.MethodAdaptor.invoke(Meth odAdaptor.java:105) at com.google.gwt.dev.shell.MethodDispatch.invoke(Met hodDispatch.java:71) at com.google.gwt.dev.shell.OophmSessionHandler.invok e(OophmSessionHandler.java:157) at com.google.gwt.dev.shell.BrowserChannel.reactToMes sages(BrowserChannel.java:1668) at com.google.gwt.dev.shell.BrowserChannelServer.proc essConnection(BrowserChannelServer.java:401) at com.google.gwt.dev.shell.BrowserChannelServer.run( BrowserChannelServer.java:222) at java.lang.Thread.run(Thread.java:619)

Here is my data source (it extends RestDataSource)

Code: public CustomerDataSource(String id) { setID(id); setDataFormat(DSDataFormat.XML); setRecordXPath("customerdoc");

    setOperationBindings();
    OperationBinding fetch = new OperationBinding();
    fetch.setOperationType(DSOperationType.FETCH);
    fetch.setDataProtocol(DSProtocol.GETPARAMS);

    setOperationBindings(fetch);

    setDataURL("/customer");

I know my web service is returning data as I can display the XML file in my browser. This doesnt appear to be a parse error (i have seen those before). Not sure what the error means. Any help is appreciated.