Yahoo Finance API not reliable !

Hello,

For a few months now I've been trying to use Yahoo Finance API for an iPhone app. Unfortunately, the YQL-based URL does or does not fetch results (randomly).

This is the URL I use :

http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.quotes%20where%20symbol%20in%20(%22AAPL%22,%20%22EURUSD=X%22)&env=store://datatables.org/alltableswithkeys&format=json

And once every 3 requests, I get this Json :

{"query":{"count":0,"created":"2013-02-11T16:13:04Z","lang":"en-US","results":null}}

If my request was wrong, I guess it would dump all the time, but that's not the case ! And I'm way below the number of connections authorized to use with the public API...

Please Yahoo Care members, advise ! (before I switch to another, more reliable API ...)

Thanks Frederic