It looks like the bitfinexUSD ticker has no data since Jul 23: http://bitcoincharts.com/charts/bitfinexUSD

This could be a change in the bitfinex API, where bitcoincharts can't get data any more (the same data source as sierrachartfeed uses). Of course if you notice something like this, you might message user tcatm on the forum or send a support email to bitcoincharts - they may not have any idea that there is a problem if it is not reported.