Problem:
 
1.  Suddenly, there is no audio output in a project even though it is playing and meters are moving.
2.  I reboot.
3.  When I reload the project, it will only play for a while—sometimes a few bars and sometimes up to the first chorus or so—and then the transport will stop and the the audio engine indicator in the control bar shows that the audio is off.  The project will always stop at this particular point (which is different in different projects).
 
At the risk of more disbelief, I think this is related to EZ Drummer 2, even though I have uninstalled it.  (Remember, that sometimes I still see "ezdrummer 2" in the synth rack even though functionally it is EZ Drummer 1.)
 
Any other ideas?  This is a serious issue.  Master copies of projects for an album are now screwed up.
 
Thanks.

Konrad, you get the award for most off-the-wall Sonar problems. I wish I had an answer for you but have never experienced anything even remotely like that. I guess the only way to get a significant clue is to find out what happens at those repeatable points in songs that makes the project stop. Normally it would be an audio engine overload, but poltergeists are a strong possibility as well. 
 
Try this:
 
Archive all your tracks except for the most plain-vanilla audio track in the project. See if it plays all the way through (and hope that it does...).
 
If it does, then keep adding tracks to see if something about one particular track causes the problem. If so, then it's time to get out the magnifying glass to see what's going on with that particular track.
 
Good luck!

http://www.resplendence.com/latencymon
 
Have you used this to see if something in particular might be causing your drop out?

Wasn't X1 real buggy?? 

sock monkey
Wasn't X1 real buggy?? 

Compared to X3, it's night and day. Still, X1d was pretty good.

Thank you for the thoughtful advice and, yes, my so-called turn-key purchase has been a nightmare from day 1. I have an album now one year overdue.

I will try the advice but how do I archive tracks I can't freeze, and what do I do with Melodyne tracks I can't bounce? (Freezing has not worked reliably since EZD2 and I've never been able to bounce Melodyne.)

I should have mentioned that CPU usage is low and with all the VIs I'm using about 4 out of 12 GB RAM (running 64-bit).

So, I froze most of the VIs thinking that would help since there has been a long standing problem with audio disapparing when there are several VIs.  (It's never the same number.)
 
After freezing, when I hit play, the transport doesn't move and the green play light on the console flashes in Pause mode.  Then I get the busy spinning thing.
 
After trying a couple of times to play the project, Sonar crashes.

konradh
I will try the advice but how do I archive tracks I can't freeze, and what do I do with Melodyne tracks I can't bounce? (Freezing has not worked reliably since EZD2 and I've never been able to bounce Melodyne.)

Archiving is not like freezing; given your problems with freezing since EZD2 I didn't want you to freeze anything. To Archive a track, you click the little A button that's grouped with the automation, freeze, etc. buttons in the track view's track headers. This basically disconnects the track from the CPU. It won't play audio when the now time passes over it; as far as Sonar is concerned, an archived track doesn't exist until you un-archive it.

OK, thanks.  On my agenda today:
1-Try the Anderton Archive method.  Maybe that will unlock the mystery.
2-Check all the inputs and outputs and see if they were somehow changed, since this is a known EZD2 issue.  (It wouldn't explain the transport issue but might explain the silent audio).
3-If all else fails: a-save off the MIDI (to desktop as *.mid) for the tracks I have changed b-save off the drum MIDI the same way, c-open an older version of the project, d-completely delete EZ Drummer and recreate the drum tracks with another VI, e-try to remember the many Melodyne edits I did to get the doubling right and to get fix the singer's rhythm, and f-start from scratch mixing since my mix changes will be lost and I will have a new drum kit.
 
Strange note: When I tried to load the project again last night, I got the message that there was no audio device present.  Audio was working for non-Sonar apps, so somehow Sonar got screwed up.  A reboot usually fixes this but it was late and I was too annoyed to mess with it anymore.
 
Just a comment: As popular as Sonar and Toontrack are, I can't believe this Ez Drummer 2 issue is just hanging out there with no resolution and no updates from either company.