Emoncms histogram data

Hello

I would like to add all measures between 2 timestamps I am not sure what the right way is.

I am trying with histogram data API option. But I am getting an error.

This is my url emoncms/feed/histogram.json?id=3&start=1474689600000&end=1474693140000

And the error is Fatal error: Call to a member function fetch_array() on boolean in /var/www/emoncms/Modules/feed/engine/Histogram.php on line 72

My feed is Power to kWh

Is it correct the way ?

Thanks

I am also facing same problem with emoncms/feed/histogram.json?id=1&start=1477239707000&end=1477412514000.

Error : Fatal error: Uncaught Error: Call to a member function fetch_array() on boolean in /var/www/html/emoncms/Modules/feed/engine/Histogram.php:71 Stack trace: #0 /var/www/html/emoncms/Modules/feed/feed_model.php(757): Histogram->get_power_vs_kwh(1, 1477239707, 1477412514) #1 /var/www/html/emoncms/Modules/feed/feed_controller.php(102): Feed->histogram_get_power_vs_kwh(1, ‘1477239707000’, ‘1477412514000’) #2 /var/www/html/emoncms/core.php(64): feed_controller() #3 /var/www/html/emoncms/index.php(156): controller(‘feed’) #4 {main} thrown in /var/www/html/emoncms/Modules/feed/engine/Histogram.php on line 71

Can someone help?