I lost the drums again, not only in PT, but with other playback software as well, after upgrading to the IE explorer 8 (Vista) update. This time, resetting the latency via the PT LatencyAdjust.SEQ file solved the problem. So, to to recap, if you have this problem:

(1) Adjust/readjust the latency

(2) Quantize durations to a higher value

(3) (last resort): try deleting the SysEx header at 1:001:00 if it didn't come from you yourself.

Paj
8^)