The troubleshooting section in both the reference guide and online help says:

My waveforms are gone, but I still hear audio; it says Busy in the corner of the clip

If your audio clips are labeled “Busy”, the waveform display has not finished drawing yet, or may be
corrupt. To force SONAR to redraw waveforms in the current project, perform the following steps:
1. Go to Edit > Select > All to select all clips.
2. On the Track view Clips menu, select Recompute Picture Cache.

My audio clips are currently showing "Busy" and I followed the above steps, but there's no such option called "Recompute Picture Cache" there.
Actually, my waveforms aren't gone. They're perfectly visible. But I can't remove "Busy," which is shown in parentheses at the end of the clip name.

Ok, I've just deleted all files in the Picture Cache folder and relaunched Sonar, and now the "Busy" is gone.
Is this the quickest way or is there actually the "Recompute Picture Cache" option somewhere? (I also don't see it in the list of shortcut key-assignable commands)

Try right-clicking on the clip, select the "Associated Audio Files" option http://www.cakewalk.com/D...N&Req=Dialogs1.20.html or open the clip in the loop construction view and the open the Clip > Loop Properties http://www.cakewalk.com/D...&Req=Dialogs2.141.html

I just blow away the cache myself

I just had this happen on every track of a project two days ago.  I did the "Associated Audio Files" "Recompute Pictures" (after searching in the manual) and all the waveforms came back to life.

Thanks both. So I tried the both methods, which worked and removed the Busy sign. But strangely, after I saved the project, restarted Sonar and reopened the project, the sign came back. This is really weird because, as I said, the waveforms were displayed without problem in the first place.

I've hardly done any audio recording since I upgraded to the X series, so I'll do more recording to see if this is going to happen very often.

The recurring "Busy" message in the waveform usually indicates that the track output isn't assigned to a valid physical output. Check your track outputs then any associated busses and see if they are assigned to outputs correctly and that they are actually present.

The project has two audio tracks (guitars) and their outputs are assigned to the master bus and I hear the guitars without problem. But to identify the cause of the problem, I now deleted all tracks and buses (even the master bus) except for the two guitar tracks and assigned the outputs directly to the stereo input of my audio interface (Quad-Capture 1-2).

Then I performed the "Recompute Pictures" to the guitar tracks and saved the project and exited Sonar. Now, I restarted Sonar and opened the project, and the "Silent Buses Detected" dialog box appeared (which didn't appear before), which says the two guitar tracks are currently assigned to a silent hardware and they will be silent. I clicked OK and loaded the project and hit the play button.......I still can hear the two guitars without problem (except for the Busy sign that once again appeared ) 

I need to do more testing. Anyway, thanks for the help.

Do you have any sends or other outputs associated with them? Any track or buss that outputs to a "dead end" will result in that message.

Thanks Karl, I thought I deleted all sends, but instead of clicking "Delete Send", which I fail to located because it's listed at the bottom of the menu, I selected "--- None ---" from the pull-down. So this time I clicked "Delete Send" and deleted the "none" send (I wonder when and what you use this "--- None ---" option for) and now the "Silent Buses Detected" error message no longer appears. Good. But the "Busy" message still recurs after I perform the "Recompute Pictures" command. Strange.

Is your sound device being used by another program perhaps Windows? That "busy" message usually indicates an output driver not available.

Thanks Karl. Will start a new thread on this Busy thing. Still can't solve it.