rrdtool module graphs generating problem

I add rrd databases from my cacti.but it doesn't work.

my Graphics Directory is =>sites/default/files
my File directory =>/var/www/cacti/rra/

when i'm going to create predifined graph it generated error message.that is given bellow.

%2Fvar%2Fwww%2Fcacti%2Frra%2F%2Fdilo_loss_51
There are no predefined graphs for the %2Fvar%2Fwww%2Fcacti%2Frra%2F%2Fdilo_loss_51 round robin database.

when i'm going to create custom graph it generated error message.that is given bellow.

warning: Invalid argument supplied for foreach() in /var/www/drupal2/modules/rrdtool/rrdtool.module on line 299.

can anyone help me?I'm new to drupal rrdtool module..