Help me out here.  I recorded a video which is in H.264 format.  I wanted to get rid of the left stereo channel.  
 
So I imported the video into Sonar X3Pro.  No problem.  Plays fine.  I bounced the original stereo audio track to two mono tracks and deleted the one I didn't want.  Then, I try to export video.
 
On doing so, Sonar says it cannot export the video.  I am not trying to change to video size or alter it in any way.  I tried using both MPEG-4 and WMV options.  I used no plug-ins or did any kind of editing to the audio except the stereo to mono as desribed above. 
 
Any thoughts?  Could it have something to do with the video format?  It seems to play without problem within Sonar.

Sonar is not the best platform to export video. Its a DAW.
 
Try exporting the audio and re-pairing the audio to video in something like QT Pro or Movie Maker and then exporting for a simple job.

From the help file Sonar Platinum 
 
Exporting video
After you’ve mixed your audio tracks the way you want them, you can export the inserted video file together with your audio tracks to create a new video file.
When you export a video, any changes you’ve made to the Start, Trim-In, or Trim-Out times determine how long your new exported video is compared to the original video that you inserted into your SONAR project.
  
Note: If you’re exporting an AVI file, the No Compression option in the Video Codec field of the AVI Encoder Options dialog box is a good choice. This choice does not change or compress your source video material. If you want your exported AVI file to be compressed, the Cinepak option will create an AVI file that plays back smoothly with decent quality. The MJPEG option will create an AVI file that does not play back as smoothly, but is a high quality format to archive a file in.
To export a video
1.
Make sure your audio tracks are completely mixed, and your video Start time, Trim-In time, and Trim-Out time are set the way you want them.

2.
Use the File > Export > Video command.

The Export Video dialog box appears.
3.
In the File Name field, type a name for your new video.

4.
In the Files of Type field, choose the kind of video file you want the exported file to be.

5.
Click the Encoding Options button to open a dialog box of encoding options for the kind of file you’re creating. Some codecs do not work: click the Help button in the dialog box for help choosing options.

  
Note: If you’re exporting an AVI file to either a 24-bit audio format or to a multi-channel (surround sound) format, set the Audio Codec in the AVI Encoding Options dialog box to No Compression.
6.
Click the Audio Mixdown Options button to open a dialog box of audio mixdown options. Click the Help button in the dialog box for help choosing options.

7.
Click Save to export your video.

Well, ultimately I just rendered the iMovie project as a .mov MPEG4 video and imported that instead.  It worked.  Must be something with Sonar and the H.264.  Maybe I'm lacking a codec or something.
 
I don't have Quicktime Pro or Movie Maker.  I don't do a lot of video stuff so was just using the tool at hand.
 
If you want to learn to play the song "Tiger Mountain Peasant Song" the video is up on youtube at:
http://youtu.be/ERRiFe7twYk
 
Thanks for your help!