Huge error at change of speed during burning

I just flashed the last firmware from Herrie (1.08 v 3-2) on my NEC2500a and burnt a TDK 4x +R at 6x. All the DVD is ok with exception of the point at which the drive changes speed (from 4x to 6x). At this point I got a Pi failure of more than 4000 (checked with other drive), and my NEC 2500 can’t even keep reading after this point.

Before flashing this last firmware, I was using Herrie’s 1.07v2b5, and also had errors (though not as big) at the points of change of speed, when burning 8x media at 6x and 8x.

Any ideas about being a problem with the hardware or firmware? I bought my NEC 2500a dirve at Newegg and came with an original 1.7 firmware (yes, not the 1.07 firmware).

Last time I burnt, I notice that the drive buffer went almost to zero when changing speed.

Any help?