I was having Midi issues when I first started using X1d, but they all went away when I rerouted my Midi cables. I have a dedicated Midi interface plus the one that is built into my audio interface. Contrary to information I was getting elsewhere, the dedicated interface was not truly Windows 7 compatible and was causing strange lag issues. It even started causing Midi recordings to show almost 128 ticks early, which was alarming. All I did was to switch to using the Midi In on the audio interface, which I wasn't using at all before, and use all the Outs on the dedicated interface. Separating things this way cured my issues and I haven't had any crashes or lag since.

Now, I'm not suggesting that everyone needs to do something like this, but I am suggesting that things may not always be working the way you think they are.

Regards,
Dan

The most frustrating MIDI issue I have is that when you create a file using a particular MIDI device setup, in my case I use a Roland piano as a controller in my small studio, and I move the file to another setup on the stage, X1 and X2 always cough up an error that it can't find the original MIDI device used. I've made the changes to the later file with the stage hardware, but it still wants me to acknowledge that the original MIDI device isn't present. It makes using a playlist set almost useless. The workaround is to assign the MIDI track to a softsynth, then freeze it, delete the original MIDI track, then save the file. That solution does work, BUT it's a hassle and I have to keep two versions of the song (studio and stage) if I ever want to tweak it. Cakewalk has been very gracious regarding the issue, but the techs aren't sure why it happens. I showed them that if you open the file in a binary reader, you'll see that the original specific driver setup is encoded into the file, i.e. "Roland Digital Piano IN, Roland Digital Piano OUT" which is different from earlier versions. The older versions didn't store actual driver names in the files other than "MIDI Dev 1 or AUD Dev 1". What's really weird is that if you export the MIDI track as a SMF, it still has that info embedded, but if you use it in different program, the info is ignored.

Glad this thread got bumped again. I couldn't find it. I wanted to say 'thanks Cliff, you are a gentleman and a scholar.' This was the first time I had used Simple Instrument tracks ever. My instinct always told me to stay away from them. I had all the things on your list checked but one. I checked that (forget which one now) and went back to Audio Track / MIDI Track and no problems. Thank you.

 
MIDI CC 7 = Volume.  Normally set to around 100
MIDI CC 11 = Expression (also referred to sometimes as volume) - makes a big difference to timbre on some libs/instruments.
MIDI CC 1 = MOD-Wheel.  This is one to keep in mind for Aria Player (Garritan).
 
Those are the main three to make sure you get sound.
 
AriaPlayer is a bit unusual in that it uses MODWheel to control volume, so you need to turn it up :-).
 
Hope that's what you're seeing, 'cos it's easy to fix :-). 
 
You should try working the CC11 for expression with many of the instruments too. 

I wish I had run into you about a week ago - I found out about CC behavior the hard way, and yes, I'm using Aria. Now I know I'm not crazy for wondering why CC11 reacted differently with different VSTis.