ntop does not display historical graph data - "Unable to create subdirectory"

Issue description:

Ntop appears to run correctly, but does not display historical graph data when viewing traffic summary data (trafficStats.html). From the Traffic Summary menu (Ntop>Summary>Traffic), under “Traffic Report for 'ethX', below “Network Load” you should find “Historical data”, with a graph icon in the right-hand column.

If you do not see the historical data graph,verify that the rrdPlugin is Active (Plugins>All). If you have an error message “Unable to create subdirectory”, verify that the appropriate subdirectory exists with the appropriate permissions. To do so, click the “rrdPlugin” link, browse down to “RRD Files Path”, and verify that the directory exists (e.g. /var/lib/ntop/rrd). If it does not exist, create it, and set appropriate permissions (if appropriate for the box you're working from - "chmod -Rf 777 /var/lib/ntop/rrd"). If it does exist, consider deleting /var/lib/ntop/rrd and re-creating it the above permissions. Finally shutdown Ntop, and restart it. The historical graph data should now be displayed.

Box: Suse 10.2, Ntop 3.2