msorrels
Just for grins I loaded up X3e (still installed) and it has the same crazy behavior with the top menu Insert Synth (not letting it change the layout) and the grayed Insert Synth in the Synth Rack that Sonar Platinum Manchester does.  So it's not a "version" of Sonar problem, it's all Sonar's.

Which to me means some setting or corruption in a settings or preset file, something that gets migrated forward (and back, in this case).
 
Do you have a lot of important stuff you'd lose if you wiped Sonar (only Sonar) off your system and started fresh ?
 

I'd be reluctant to wipe Sonar and start again because I have a hunch that all of this may be to do with something with Sonar's scanning of plugins and if that is related to one-or-more specific plugs (3rd party or CW) then it's not just Sonar that needs to be wiped and reinstalled. Just a thought, though, for which I have no evidence whatsoever.

Paul #29: I admire your persistence on this one! I don't know whether I'm fully understanding what you are saying in #29, but I don't seem to get the same results as you. Whether the button is left blue or not seems to make no difference. I have found only two ways of reliably blowing up Synth Rack: selecting "default" layout in Browser Synth tab (i.e. Synth Rack): or selecting "default" via (main menu) Insert - Soft Synth. Oddly, in the latter case, the main menu is happy to be set to "default" (i.e. it works fine and can later be reset to a specific layout) but the collateral damage is that Synth Rack is then crippled until I go to regedit and fix the blank key.
 
I have already filed a bug report (although I don't have much hope that this is persuasive of the Bakers - I'm guessing it needs at least fifty bug reports on a topic before they take it seriously).

Okay, so in the past when looking at this I'd reset my VSTs in the Plugin Manager and then have it rescan.  Doing this, I'd never get my insert synth option back, but I never did it a single path directory at a time.  I have 5-6 directories in my VST scan list (VST3, Cakewalk dirs, my VST2 32-bit dir and my VST2 64-bit dir).  So I wiped my VST inventory registry and had nothing in my VST scan list and started Sonar up.  It found 22 plugins, all DirectX, and my insert synth menu item was back! 
 
I then started to add one directory at a time and rescan.  I put the Cakewalk dirs back, no problem.  I put the VST3 dirs back.  No problem.  I added my VST2 64-bit directory.  During the scan one plugin crashed, Tunefish64.  Some free synth I think.  I just moved it out into my Bad VST holding dir, don't think it had anything to do with this.  Re-did the scan and my Insert Synth menu item was gone!  So I've narrowed it down to one of my VST2 64 bit plugins.  A file search for *.dll on that directory says 671 DLLs, one or more of which is the problem, or perhaps it's just the sheer number of them. 
 
I'm pretty sure I can turn off the rescan on startup option and then just chop parts of the VST Inventory out of the registry in order to narrow this down.  But it's going to take some time.  And it still just may be the total number or it might have something to do with the path.  I do notice some issues in Procmon (a Windows Developer tool) when Sonar reads the registry complaining about the entries being too long.  My plugin dir has a number of sub-directories, which makes for some long entries in the VST inventory.
 
I may have some time this weekend to see if I can narrow this down some more.  Considering how little this bug effects me I've certainly spent a lot of time on it though.

Matt, I don't doubt your sincerity nor your findings, but it would be a braver soul than me who would download registry entries and then insert them into their own registry. Sorry. I suggest you take the contents of your post and convert it into a bug report and let the Bakers have it with your .reg files and see what they make of it.

.reg files are plain text you can visibly check everything it's doing in notepad.  But I also understand not wanting to take any risk to verify this.  The information is here, Cakewalk is welcome to use it.  But I won't be reporting anything to their support, they burned that bridge on this very issue.
 

I'm wondering whether I have one particular plug-in that somehow prevents Sonar from creating the default on the fly and that Sonar's code is not robust enough to take such a thing in its stride ... but wondering is as far as I am going to take it, because I just don't have the time to spend finding the rogue by any process of elimination, especially since there may be more than one rogue.

I regret to say that I have not found any way to fix this other than to go into the registry via regedit and fix the corrupt keys. The fix lasts only for so long before Sonar corrupts the keys again, so this is not a practical solution. The Problem Report CWBRN-45498 that I made at the beginning of February still says -

Status Information

The current status of your report is
New
This is a new problem report. It has not yet been reviewed by Cakewalk.
 
This makes me wonder what Cakewalk actually does with Problem Reports if after nearly 4 months no-one has even looked at it. None of the other methods for inserting a soft synth is particularly workable either. The newish Add Track thing looked promising but its bizarre way of ordering the list (without the ability to use Layouts) makes it unattractive, too.
 
I don't feel well supported by the Bakers here, I'm sorry to say.

I wonder why the keys are getting corrupted in your cases? I have never seen this behavior and it makes me wonder if there is an antivirus that is intercepting Sonar's write to the registry and corrupting it?
 
Regards,
Dan

Windows Defender probably isn't the cause...so I agree with your point. It is strange that it isn't more common. I have well over 600 plugins and use a custom layout.
 
Regards,
Dan

Well, I 'm sorry to hear that Davec, but perhaps if anyone experiencing this bangs in a Problem Report, the Bakers may read one of them and take some action. [hope triumphing over experience again]