ntop, rrd a Invalid alpha

[konference.labut at seznam.cz]

zdravim,
narazil jsem na problem s rrd pluginu v ntopu.
Network Load Statistics se nezobrazi s poznamkou 
"NOTE: this page is not operational when the RRD plugin is disabled, 
misconfigured or missing. Please check the ntop log file.".

V logu je
Sep 18 09:54:46 freeqwe ntop[8534]:   **WARNING** RRD: 
rrd_create(/var/db/ntop/interfaces/sk0/throughput.rrd) error: Invalid alpha: 
must be between 0 and 1
Sep 18 09:54:46 freeqwe ntop[8534]:   **WARNING** RRD: 
rrd_update(/var/db/ntop/interfaces/sk0/throughput.rrd) error: 
opening '/var/db/ntop/interfaces/sk0/throughput.rrd': No such file or 
directory
atd ...

vubec netusim co to ta 'Invalid alpha' je, googl moc zdilnej neni.
prosim, muzete me nasmerovat spravnym smerem?
FreeBSD 6.2-RELEASE-p7

dik
Jan Labut