... Anyone have any other ideas? The problem seems to be getting worse and effecting other projects that don't have as much going on in them, at least as far as plugin count is concerned.

cleared your picture cache?

pwalpwal - No, how do I?

check you prefs for the location of the picture cache
close/exit sonar
navigate in explorer to the location
delete all the WOV files
 
if you search the forum (and extend the date range for the results, or just use google instead) you should find plenty of info
 
good luck!

pwalpwal - Tried this and thought it worked for a few minutes, as I got sustained playback longer than before. A few minutes in, the same old thing happened. What are the WOV files and why would you delete them but not the other files in the Picure cache folder?

you can try deleting the other files as well, same routine as above
they're used for the little "preview" wav images displayed inside sonar

I might be wrong, and probably am, but once the recording gets sufficiently complex, given the limitations of your cpu etc., you have to increase buffer size of the audio card.  I don't think you can do this WITHIN Sonar, but need to shut Sonar down, then go to your AtoD card and set the buffer there to something like 1024, then reboot Sonar.  That is what I have to do when mixing with a lot of plugins.

I had a dropout problem once on a particular project. I clicked on "Help" in the Toast notification and went through each of the options. I forget which one solved the problem, but one of them did and also solved a slow startup after hitting play which I thought was inherent in the program.

I had forgotten that while an ASIO Buffer Size of 64 usually was OK for one of my audio interfaces, 32 was pushing it - and after updating to RC1, I began having weird audio engine dropouts AND one or both midi controllers being lost to Sonar - even though they were still connected and Windows and Sonar were both indicating they were working fine.
 
As soon as I bumped back up to 128, all of the weirdness went away, and I left a project looping for the past 3 hours and had no issues, whereas with the smaller ASIO Buffer Size settings of either 32 or 64, I would get an audio engine dropout or one/both midi controllers would be disconnected to Sonar when they weren't OR the audio engine would dropout.
 
So - just a thought to maybe bump up the ASIO Buffer Size a tad, to see if it helps.
 
Bob Bone
 

I am not sure if this is in the category - sometimes when I press play or record it will take some seconds before anything happens.  Then it will be instant after I try it again.  Did not have this on earlier versions than Manchester.