I don't know if I should submit a bug report on this, but I figure it must be such a common thing that maybe somebody in the community can help.  I am running Sonar Artist with the 2016.05 update 1, although this problem goes back at least a few months.
 
A couple of months ago I switched from using the WDM drivers to ASIO for my UltraLite MK3 in Sonar.  I soon found that I couldn't open any project files that had been saved with the WDM drivers unless I first switched back to WDM, opened, and then switched back.  When I say "couldn't open", I mean that Sonar would hang and I would have to kill off Sonar.  Opening in "safe mode" resulted in a question about plugins, but then it would still hang.  Regardless, I had a work around and I just went forward.
 
Now I am experimenting with a new UltraLite AVB using its ASIO drivers.  When I open a file that was saved with the MK3 (and different device names), I get a "Missing Audio Devices" popup asking me to map to new devices, but Sonar is frozen.  I can't select anything or click a button.  Again, I have to kill off Sonar.  Safe mode doesn't make a difference.
 
I don't know if these two issues are related, but I would like to know if other people have experienced this.
 
Thanks in advance -- I have lots of projects that I am working on and not sure how to proceed.
 
 

So I did submit a bug report on this and after several weeks received an apology for no response (and a discount coupon).  Then nothing.  
 
I may try to reinstall my old interface (and drivers) and migrate these manually, but I see this as a major bug.  What if my old interface had burned out?  
 
With no substantive response from Cakewalk I'm thinking maybe it is time to jump ship and go to another DAW.  Some of that is "grass is greener" -- you don't really know what support is like until you need it -- but according to other posts on this forum it looks like Cakewalk support is dead.
 
It certainly is stopping me from taking "lifetime update" seriously.
 
 

If it's a bug it must be new as I have used 4 different interfaces over time and Sonar certainly never has frozen. Projects done on my long gone M Audio fast track the Outputs get changed from 1/2 to SPDIF so some weird reason. 
 
I record live gigs to my laptop in WDM mode using my Tascam us1641 then dump the projects to my main DAW which uses my Scarlett 6i6 in ASIO without any issues at all. All that happens is the inputs change from all the multi channels to scarlett stereo 1. The outputs seems to stay 1/2 with this combo of interfaces. 
 

I don't recall anything even remotely like this being reported before. Generally that means it's something system-specific, and the issues would suggest driver problems or interactions. The first thing I'd do is remove any other audio drivers on your system, like if you have ASIO4ALL installed (a known source of multiple system-specific issues - sometimes it works, sometimes not, sometimes just having it installed screws things up) and also, check the tip for Week 35 in "Friday's Tip of the Week." These "HD Audio" drivers can really wreak havoc with a system.
 
As to support, I'm sure there's nothing in their database about this. Cakewalk has hired/is hiring more support personnel but it takes time for them to ramp up, particularly because the support structure was changed recently to avoid people having to wait on the phone. FWIW most of Cakewalk's support issues involve third-party plug-ins and drivers, which are not always easy to duplicate.  
 
 

Try renaming "AUD.INI".

Audio Driver settings are stored in that .ini file, and SONAR will build a new AUD.INI based on the settings of your current audio interface upon the first start.

AUD.INI is located in
C:\Users\...\AppData\Roaming\Cakewalk\SONAR Platinum
 

Klaus's suggestion would be the first thing to try, but if problems persist, don't overlook having drivers that serve no purpose interacting on a system level.

Thanks for the suggestions.
 
I did try renaming Aud.ini with no luck.  
 
I will look more into HD Audio (which my mother board has), but all of those drivers are disabled and have been throughout.
 
I went ahead and installed my other interface and drivers, and yes, my projects open just fine.   I may need to remap all audio to "none" or to the new interface and see if that works.
 
Don't feel like I really have a solution and can't really take the time to reinstall Windows from scratch just to see if the "waxy buildup" of Windows is part of the problem.  

I have spent some time on this over the last week, but really no luck.  Disabled HD audio at the motherboard level didn't work.
 
I was able to install the drivers for the old interface which lets me open the old files, but I can't remap them to the new interface.  I thought I could map them to no input/output and save them to create projects with no knowledge of the interface, but it doesn't work.  In fact, once I do that, I can't re-open the files regardless of the interface that is configured (the same "hanging" behavior).
 
Because Sonar has given me no help whatsoever, the logical next step is to try a clean install on another machine (or a clean install of Windows and then Sonar on this machine).  I'm not terribly thrilled about that.  I really don't have the hours to burn.
 
 

Before re-installing SONAR, try a full repersonalization by holding down CTRL and SHIFT while opening SONAR. This will overwrite files in your user directory and reset some of the registry settings back to default. If you have custom files you want to save make a copy of your user directory first. The user directory in this case is "%appdata%\Cakewalk\SONAR Artist." Although a clean reinstall of SONAR is pretty quick. I would be surprised if either makes a difference in this case. May also want to try a roll back before clean reinstall.

Thanks for the idea, but the repersonalization didn't make a difference.
 
I agree that a clean install of SONAR won't make a difference either, I'm suggesting a clean install of Windows.  That doesn't have to take too long, but I don't have the luxury of a having a DAW-only system so there other software applications to install (some of which are complex).
 
Maybe I can get to that this week.