Client object model (javascript) - How to use get_listItemCollectionPosition for paging?

Hi,

This is my code:

When I call the function to get the items, it fails (doesn't go to the fail function, it goes into the success function but crashes when I try to get the position object), and I get the error:

[13:17:57.273] Error: The property or field has not been initialized. It has not been requested or the request has not been executed. It may need to be explicitly requested.

If I don't use the context string, then it works ok. But I need to get the base permissions, as well as only get some of the fields.

Does anyone know how to fix this?

Thanks.

// occurs when the document is ready
$(document).ready(function() {
	// wait for the sharepoint javascript libraries to load, then call the function 'Initialize'
	ExecuteOrDelayUntilScriptLoaded(runCode, "sp.js");
});


var listItems;                   // The list of retrieved items.
var query;                       // For paging, reuse the same query object.
var targetList;                  // The list from which to retrieve items.
var clientContext;

function runCode() {
    clientContext = new SP.ClientContext();
    web = clientContext.get_web();  
    targetList = web.get_lists().getByTitle("Marketplace");
    query = new SP.CamlQuery();
    var CAML = "<View><Query><OrderBy><FieldRef Name='Modified' Ascending='FALSE' /></OrderBy></Query><RowLimit>5</RowLimit></View>";
    var CS = "Include(EffectiveBasePermissions,Title,Description,Office,Category,Contact_x0020_Number,Second_x0020_Contact_x0020_Numbe,Contact_x0020_Email,Web_x0020_Site,Author,Editor,Created,Modified,ID,Attachments)";
    //Specifying the RowLimit will determine how many items will be fetched in one call to the server.
    query.set_viewXml(CAML);
    listItems = targetList.getItems(query);
    clientContext.load(listItems,CS);
    clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded),Function.createDelegate(this, this.onQueryFailed));
}

function onQuerySucceeded(sender, args) {
    var message = "Titles, two at a time:\n";
    var listEnumerator = listItems.getEnumerator();
    while (listEnumerator.moveNext()) {
        message += "\nTitle=" + listEnumerator.get_current().get_item("Title")
    }
    alert(message);
    //Gets the id of the last element from the returned collection along with the query.
    var position = listItems.get_listItemCollectionPosition();
    //Position will be null if all the items in the collection are fetched and there are no more items to be fetched.
    if (position != null) {
        //If more items are to be fetched, make a second call to the server and fetch the next group of items.
        query.set_listItemCollectionPosition(position);
        listItems = targetList.getItems(query);
        clientContext.load(listItems);
        //Call the same function recursively until all the items in the current criteria are fetched.
        clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded),Function.createDelegate(this, this.onQueryFailed));
    } 
}

function onQueryFailed(sender, args) {
    alert('Request failed. \nError: ' + args.get_message() + '\nStackTrace: ' + args.get_stackTrace());
}