I'm not sure if this is a Sonar Issue or Toontrack Issue.  I have a Yamaha DTX400K e-drum set that I use to trigger Toontrack's Superior Drummer through Sonar X2.  I use a USB attachment from the kit to the computer.  When I open a new project the kit syncs up and I can use the kit to trigger Superior Drummer.  However, when I reload the song file, I can't get the e-kit to sync up.  The drums will play through play back, I just can't trigger them.  I've always checked preferences the ekit is listed as a device.  
 
I've had the same issue with a keyboard midi controller (Alesis).
 
Any ideas?  Thanks.

It sounds like Sonar is loosing your Drums as a MIDI device. If I forget to turn my Drums on, then Sonar always shows a dialog box when opening to tell me there is no DTX midi device. 
Are your drums on before loading Sonar? do you get the MIDI in/out dialog? 
You should if it looses connection. 

Cactus, thanks for responding.  Yeah, I make sure the drums are on before I open Sonar.  And when I look in the preferences, the drums are listed and checked as a midi device.  If I turn the drums off or on while Sonar is running I get the dialog, but it still doesn't work.  Very frustrating. 

It is probably a simple mismatch of MIDI channels.
 
Look for the MIDI input channel selection and find out what channel the e-Drums (and your keyboard) come in on.
 
 
best regards,
mike