#26 rrd graphs stop working

[freepower31]

For some reason, the rrd graphs stop showing usage. The time is not the same, could be after 10 minutes or 30 hours. In the logs, I am receiving the following error **ERROR** Buffer too short @ rrdPlugin.c:3216 (increase to at least 581). Stopping the rrd plugin and restarting does not correct the issue, I have to restart ntop. Any ideas? Thanks for the help