Hi,
@jgottlieb:
I found a thread that was able to fix the issue at least for me - http://forum.pfsense.org/index.php/topic,10855.msg69541.html#msg69541
yep, that thread was started by me, actually. And yes, it was effective deleting /var/db/rrd/*-quality.rrd files one time before, but not always, since mid of Jan. I know that 2.0 is still -AA quality and ways to go, needs some attention for this kinda monitoring issues, however.
cheers,