problem rrd file : values in last_ds instead value

[pologfi]

Hi,

My values are returned in rrd file in last_ds instead value :

rrd_version = "0003"
step = 300
last_update = 1299231383
ds[free].type = "GAUGE"
ds[free].minimal_heartbeat = 120
ds[free].min = 0.0000000000e+00
ds[free].max = 1.0000000000e+03
ds[free].last_ds = "448"
ds[free].value = NaN
ds[free].unknown_sec = 83


448 is my attempt value.