I've had red error spikes on my kprobe 2.23 scans as well, when using external usb 2.0 LTR-52327s (either via Ahead/Nero WNASPI32.DLL or via SPTI).
The problem seems to be related to high cpu activity, during which the kprobe2 scanning throttles down in speed (or at least the speed indicator in kprobe window slows down).
I'm running a very well optimized Athlon 3400+ with nforce3 board 1 GB of RAM, fast SATA discs and no nVidia IDE drivers.
However, I'm not getting these spikes all the time, but I do get them regardless of whether I use ASPI or SPTI. I've only had it happen with the external drive though (internal drives on the IDE/ATA bus are always fine).
Can you tell me which software you were suspecting for high cpu activity?
Also, if you have any other clues/ideas, please chime in again.