I am getting the following exception       
Specified argument was out of the range of valid values.
Any Ideas??..
        IObservable<StockQuote> GetQuotes(IScheduler scheduler, IEnumerable<StockQuote> quotes)
            // TODO: Create an observable source of stock quotes
            // HINT: Use both the scheduler and the quotes and think about how to create sources which are like events          

          return quotes.ToObservable<StockQuote>().ObserveOn(scheduler);

        IObservable<object> Query(IObservable<StockQuote> quotes)
            // TODO: Write a query to grab the Microsoft "MSFT" stock quotes and output the closing price
            // HINT: Make sure you include a property in the result which has a type of DateTime

          var filteredQuotes = from quote in quotes
                               where quote.Symbol == "MSFT"
                               select quote;

          return filteredQuotes;