incomplete midi exports

I have struggled for days now trying to get a simple piece with four instrument tracks to export as a type 01 midi file. The resultant export consistently creates only two of the four tracks, and I cannot find any difference in the track setups (except the instrument chosen in Sonic LE). Can anyone point me in the right direction here? I really need to send this file out soon and cannot sort out the issue. Many thanks for any assistance.
Cubase 6.5.0
Win 7, 64 bit running 32 bit CB installation.

Just in case someone else has this happen, I solved the problem by copying the midi info to new instrument tracks, deleted the originals, and the new export attempt was successful. Somehow two of the instrument tracks were corrupted, but how I cannot say, as there was no visible parameter disparity from the other two tracks.