Buffer Underrun Problem on Plextor 16/10/40A

[blackmage]

I just bought a Plextor 16/10/40A EIDE writer. I can burn perfectly with 12x, but when I switch to 16x, the buffer underrun problem occurs. I'm using Nero v5.0.4.8 with burn proof. If I disable burn proof and burn cds in 16x, they are all failed after 20sec of burning. I tried to defrag and closed all applications before burning but it was no use..... So can someone plz help!!

My system is
K7 800mhz
160 SDram
abit KT7 Raid
Maxtor 20gig HD (connect to ATA-100 Controller)