I spent a really stupid amount of time laying down a piano track for a new song I'm composing.  I used take lanes to record each performance, keeping some and deleting others, to get a good mix of possible ideas.  The last few takes were, of course, the best, and represented the latest development of my composition...
 
...and are now gone.
 
I had no warning, nothing seemed to be wrong.  I saved my file and exited Sonar.  When I came back and reopened the file, I found the majority of my takes had vanished.  What gives?  I now have to HOPE I can remember what I played last time, and try to reproduce it.  
 
I'm working with Sonar X2a Producer and Windows 7, V-Studio 700, Midisport 8x8/s, Oxygen61 keyboard.  I'm using samples from EastWest and the latest Play engine.  The takes were all MIDI data, recorded to the Play instrument track.  There was no audio data.
 
Thanks,
Heather

I can't speak to the fact that the takes you wanted to keep disappeared. That's pretty unusual.
 
I do believe that to keep things orderly, if you delete take lanes, it actually deletes the underlying midi or wave files as well. This is useful if you are really DONE with data and want to be rid of it.
 
I usually MUTE take lanes I don't want, and when I get a take I want to work with, I usually move it to another track and mute and hide the track with all the other takes I might want to return to.
 
I'm really sorry you lost a great take! I hate it when one gets away!

gswitzI'm really sorry you lost a great take! I hate it when one gets away!

 
Thanks.  Yeah, it was really weird.  Not being the world's best pianist, I'm not overly concerned about losing any brilliant performances or anything.  It's the ideas I hate to let get away.  My main concern is this might be some sort of bug that could pop up again sometime.  Because that would be bad.  Hopefully it's just a one-time fluke.  
 
Right?  
 
~ Heather
 

Try changing the simple instrument track to a normal synth and midi pair. See if that helps in the future. I don't use the simple instrument tracks at all myself and have never had midi data go missing.
 
If you have the auto-save feature enabled you might find a copy of your project that has some or all the missing midi data in the project folder.