Have you tried updating the firmware?
Official NEC DVD Firmware Downloads
You could also tried some hacked firmwares, but best to try the official NEC ones first.
Let me know if this solves your problem. I've got a friend with a Dell version of the NEC ND-2100AD that has the same problem...he hasn't tried the firmware update until he knows for sure...tried to convince him that he's got nothing to lose but he wants proof.