99% of the time whenever I want to add a new VSTI instrument to SONAR I do the following:

1. Click on the Synth tab in the 'Media Browser'
2. Click the little '+' sign in the upper left corner
3. Go to 'Insert Synth' and browse to the desired VSTI instrument from my custom menus.

 
Since the latest update, the 'Insert Synth' option can now become permanently grayed out and can no longer be selected.

 
I had actually encountered this same bug in past SONAR versions and discovered that it seemed to be related to the number of VSTIs that were in my Custom Menus. At somewhere around 255 VSTI plugins the 'Insert Synth' menu option would become ghosted out. Previously the only workaround was to reduce the number of plugins in my custom menus until the 'Insert Synth' option reappeared.
 
Since the latest update I have discovered that selecting any of the new 'Sort By...' options immediately causes the popup menu to become grayed out. Since there is no custom menu involved this time, the selection is not only permanently grayed out but you can no longer switch back to any of your custom menus via the Plug-in Layouts option. The only workaround that I have found is to go to your plugins folders and physically reduce the number of VSTI plugins in that folder until it gets below 255 vsti plugins. I did this by using .ZIP to temporarily compress some folders since SONAR can't scan zipped folders. Once you are below 255 VSTIs again, you can them switch back to one of your custom menus. 
 
Keep in mind that I am only referring to VST Instruments. So far I haven't encountered any similar issues with VST effects and also remember that effects can't be inserted using this popup option.
 
BTW, the new Categories customization features are seriously slick. I can't wait until this bug is fixed so that I can actually take advantage of them.
 
Regards,
-e.B

I thought I read somewhere this wasn't a sonar bug but a windows limitation.
I could be wrong. but wow, 255 synths. your my hero .

Hey e.b. That's a lot of synths dude! Imagine the size of your studio if they were hardware:)
This is the first ever forum problem I wish I had.

That s why i only use templates .".

You have 255 synths?
 
You hear things we don't man.

I remember reading something about this as well...I guess there are so few people who have 255 VSTi programs it's not something that comes up much.

This isn't the Windows bug (which is a whole different thing).  This is a problem with how Sonar builds the add Synth menu.  Which is odd, since there are other add synth menus (for example on the track view) that aren't effected by this bug, just the synth rack's add button.  I think Cakewalk could fix this, I believe it isn't that hard to reproduce (and have sent them detailed steps with registry settings that should let their testers reproduce this without any real tricks at all).  So far Cakewalk has ignored this issue.  Sad really.
 

I guess there aren't too many people with over 200 vsti plugins...

We always need remember that the Bakers have to address items affecting the largest numbers of users first...

So I imagine they will get to this at some point too...

I'm sorry it's causing you difficulty and glad to know that you can use one of the other insert synth locations as a work around...

It appears that I've been having the same problem.  Insert Synth button greyed out.  I can usually resolve it by restarting Sonar.  For me, it just seems random, as to when the the problem arises.  Really a pain to the workflow though. 

Do you have a similarly large number of plugins?

If not, the bug might be something common to a larger number of users...

Please note, I meant no offense to anyone in my previous post.... I know what it is to be inconvenienced by something big or small... An itch you can't scratch...

My apology if I did offend anyone...