Cacti fresh install on CentOS have graphs with no values

[imax36581]

recently i installed cacti in centos 6 using yum.
it seems everything is ok but the graphs(including the default linux cpu/mem,..) are empty with no values.
i checked the permissions. currently the permission of cacti directory and its subdirectories are 777(just for testing)and paths are correct.
the only changed that i made was changing the polling interval to 1 minutes(graphs not shown in default 5 min interval neither).

i attached the last lines of my Cacti logs.

is there anything that i missed

thanks in advance