Parse.com: Adding sorting causing error in query

Below is some Node/Express code that runs fine as long as my sorting order isn't specified. Anybody know why it won't let me sort the query?

getBusiness("example.com");

function getBusiness(domain) {
    var Businesses = Parse.Object.extend("Businesses");
    var businessQuery = new Parse.Query(Businesses);
    businessQuery.equalTo("AppUrl", domain);
    businessQuery.first().then(
        getNavigation,
        handleError.bind(null, "error getting business"));
}

function getNavigation(business) {
    var Navigation = Parse.Object.extend("Navigation");
    var navigationsQuery = new Parse.Query(Navigation);
    navigationsQuery.equalTo("Business",business);
    navigationsQuery.ascending("SortOrder"); // When this isnt commented out, error 
    var promises = [];
    navigationsQuery.each(function (navigation) {
        promises.push(processNavigation(navigation));
    }).then(
        function () {
            Parse.Promise.when(promises).then(
                renderResult,
                handleError.bind(null, "error processing navigations"));
        },
        handleError.bind(null, "error iterating navigations"));
}

...

There are obviously two tables: Businesses and Navigation. And Navigation has a column called SortOrder that I'm attempting to sort by.