This is probably an Antares problem, but I thought I'd post it here in case someone else has run across this or has a fix. 
I have tried install/uninstall/reinstall (and re download) the Mic Mod EFX 64 and it didn't help.  It is activated on my iLok.  I have other Antares VST2 plug ins and there is no problem with them. 
 
If I try to access the Mic Mod EFX 64, Sonar will immediately abort (I've sent the report to Sonar). 
The error report:
A fatal error has occurred
C:\program files\common files\vst3\Mic Mod EFX x64.vst3
A crash dump has been created.......
Exception Code C0000005
Address: 0000000016FEC186:000000000000065:000000000000065
 
I've seen a report of the same problem with another Antares VST3 application (different application) and Sonar X3 on the Antares forum.
 
 
 
 

I had similar problems with older IK stuff in X2.
It appears to be "fixed" in X3, the old stuff is again working.
But this is a x64 vst3 plug.
99 versions of C++, think that has anything to do with it?
The bear dances badly, but he does dance.
Maybe this is where Apple shines, a little tighter control over 3rd party development?
 
Tom

Darn! I just bought that! couldn't resist the $29 deal, especially as one of the mics they've modeled is my go to mic.... a CAD Equitek E100S... the only mic engineered and currently made in the USA!  Unfortunately computer's in the shop for an upgrade or I'd check this, Tom
 
BTW, unlike in the past, I've gotten quick responses from Antares support over the past year to several queries so I'd just shoot um an email...
 
w

The installer won't load the VST dll files for me. Grrrrrrrrr!

Same issue here. Just bought the $29 deal. As soon as I try it, sonar crashes.

I have Avox Evo and was looking forward to moving to VST 3 and x64 but I had no luck getting the Avox 4 demo to install and run. I've uninstalled the demo and will stick to the 32bit Avox evo suite.

I got a workaround for this.  Use the  VST2 and it works OK. 
 
What you have to do is go to Sonar and add the VST2 path (in VST settings) and then change Sonar to NOT hide related VST2 plugins.

 
The VST2 version is located here:
C:\Program Files\Common Files\VST2
 
This doesn't fix the VST3 problem, but the program works OK as a VST2
 
Jack
 
 

Another update.  The tech support person I've had correspondence from at Antares over this problem advises they are aware of the VST3 problem and "working on it".

I resurrected this thread.  The problem has been fixed in the X3D release.

Great!