Upgrade failed with 21061, 21286, 21676, 22118.
I found that my NetGear WNR2000v3's CPU is AR7241 rev 1.1, but DD-WRT's webpage said it's AR7240.
Maybe my WNR2000v3 is different from DD-WRT programmer's so that could be the reason which made the later firmwares incompatible to my router...