This has started to happen to me on and off for the last few months, and now it's in a very simple project with very little else to interfere:
 
I have a project with one midi track and one audio track. The audio track has four takes, one clip each take. The the audio clips are about ten seconds long. The midi clip is about one minute. No effects or other data in the project. Playback was working fine.
 
Using the length change process, I shortened the audio. Now, playback does not work if I set the start time prior to or in the middle of the audio clips. Sonar does not respond at all, using either the Space bar or the play button. If I try to start playback past the end of the clips, it plays back fine. Like I said, I've seen this behavior in another project lately intermittently. I just created this dummy project this morning and am running into this same issue now. What's going on?
 
EDIT: Backing out of the recording and doing it again, it now will play back prior to the clips as expected, and at some points within the clips, but there are points that will not play back if I try to start from there, always within the clips.
 
For example, if my clips start at bar 2 and end at bar 6, I can start playback at bars 1, 2, 3, or 4, but if I try to start playback at bar 5, it will not respond. Weird.

Bump
 
I'm still having this trouble. Without diving into specifics, my project with lots of audio clips has a lot of problems with playback. Depending on where the start point is set, sometimes it just won't play. Sonar ignores the Play command entirely. I need to move the start point around to find a place that will start. Although the no-start points seem consistent, meaning it will never start from certain places, I can't seem to find any logic behind where those bad start points are. Anyone ever seen this? It's happened to me in two projects now. 
 
The audio engine also stops unexpectedly very often, sometimes in the same place every time.
 
Many of these audio clips have been edited both by transposing and by duration changing. I have multiple takes per lane. No other data in the projects. I had some reverb in there, but disabling all effects does not fix the problem.

Try bouncing your edited clips to themselves.

Just guessing/speculating:
Could it be possible that the time setting during the length-process plays a role here? IIRC , changing tempo in projects with audio you need to have time setting set to "absolute". Changing the length of an audio clip is practically same as changing the tempo. If time is not "absolute" SONAR may create confusion about where the clip actually starts.  
As said: Just speculating.