I started a project in session drummer 3 in X2. When I migrated over to X3 everything looks and behaves fine in the  project EXCEPT I get occasional snare notes dropped (at least that is the only drum that drives me nuts enough to worry about).I tried unlinking the clips, thinking that perhaps it has something to do with step probability I then went into each and every clip to make sure. Probability 100% on everything. Is there something else I can do to attempt to fix this before throwing the whole track out and starting over. I'm thinking event list view, but don't know what to look for. Is step probability a controller? Is this a bug I'm unaware of? I thought step probability is event dependent but if I get one of the"dropped" notes to play, it usually drops another in the clip.This can't be a polyphony thing, can it? there's never more than 3 things happening at once.

Increase "Prepare Using nnn Milisecond Buffers" value in Preferences > MIDI > Playback and Recording from 250 to 500 or 750.

That sounds like the famous MIDI buffer problem.  I used to have that all the time but not anymore.
 
Someone else can correct me if I have forgotten the wrong place to fix this, but under Preferences | MIDI | Playback and Recording, I have a 1200 Millisecond Buffers in the playback section.  (I also have Number of Buffers = 64 in the record section, but I don't think that's related to your problem.)
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Also, while we're at it, I always set the Audio | Drivers | ASIO Panel to a low number for recording and playing back MIDI (like 3 or 4 on the scale) and recording singers, and a higher number (like 6 or 7) for mixing *after* all synths are recorded or frozen.  Low = less latency/delay; high=reduced pops/clicks/audio drop-outs.  This is not your problem but you may enncouter this as well.

You guys rock! I use a lot of midi hardware and virtual instruments, so you would think that I would have gone to that right away. But I almost forgot that I had imported this into X3 and it's therefore my first X3 project. Midi buffers were set to default value. Raised to 500 and everything started playing. Sometimes it's hard to get an objective look at the escape route when you are in the burning building. I almost erased a track that I worked on for a long time. I would have recreated it , played it back and gotten the same result before even considering that it was a system issue, not a glitchy track.
THANKS AGAIN!
Tim

Yay! Forum folks rock again!
 
It still baffles me as to why those buffer sizes were downsized from 500 to 250 in the first place.
 
Congrats on it all working for you now.
 
Bob Bone