Hi.  Not sure why but a particular project file is having issues.  No other file.  It has audio and midi content with soft synths.  Nothing over the top in terms of track count.  Autosave takes about 2-3 minutes.  One midi edit will result in stalling for over 5 minutes. The file has become unusable.  is there a way to fix this?

What happens if you load the project in Sonar's Safe Mode, and skip the loading of all plugins?
 
This would let you know if perhaps one or more of the plugins is not playing nicely in this project, and would give you a starting point for figuring which one(s).
 
If things work OK with no plugins, try loading in Safe Mode again, loading only the 1st plugin, repeating the load in Safe Mode and an additional plugin, and so on, until you figure out which one is the last loaded when problems begin showing up.
 
Then, load again, up to that 'bad' one, skip it, and load the one past it, etc... to see if there are any others.
 
Just a thought - all predicated on the project working when all plugins are first skipped.  If problems show up when you DID skip all plugins, then there may well be some sort of corruption, but let's start with the hope it is a plugin and go from there.
 
Bob Bone
 

So you can open the project I assume.
You issue is that it works but it is far too slow?
Try opening it in safe mode within Sonar, if that is no issue then maybe you can find a particular plugin that may be at fault.

Also temporarily disable antivirus.
Cheers...

Or what Bob said looks like we posted at the same time more or less :)

Was audio snap used in the project? May want to check the physical size of the cwp file.

Thanks very much.  An odd thing is that the file size for this project is about 10x the size of a project with more tracks.  Not sure why that is.

Ruling out plugins is a good idea though. The other thing you could do is make a bundle file, open and extract it to a new project.

If audio snap was used in the project it may have blown the cwp file size out. Try bundling the project, then unbundle the file in a new location. This should rebuild the project reducing the size. Bundling will remove all audio snap markers from the project.

The bundle option didnt work but there is a rogue cello midi track that is blowing up the file size.  Just deleted it and will recreate it.
 

All of the above answers are possible solutions. I have had the audiosnap problem before. After syncing 8 tracks of a shakey drum track, every time I opened the file or exported it would take between forever and not exporting at all unless I took off fast bounce.
 
I have had other files that I never could figure out what certain problems were. In that case, usually (maybe always), I would open a new Sonar file and copy the information into it and it would be fine.