I had the same problem in X2. After some aggravation, I reinstalled the session io driver and made the following changes in Sonar via Edit -> Preferences
Playback and Recording -> Driver Mode -> ASIO
Audio Data -> Change Record and Render Bit Depth to 24, Import stays at 16
Click Ok to save
My guess is the ASIO driver only wants to work with 24 bit files and the left channel must be used as the timming device (Forced 24 bit)
The other drivers (i.e. WDM) sounded really bad when recording which supprissed me so I was forced to figure out how to get ASIO to work.

You do realize the thread you posted to is more than 4 years old with the next more recent reply over 2 years ago. If you have an issue, you might want to post in the X1/X2 forum above this one.