VST 3 instruments from Arturia also do not work in X3. I think there are some others. There are several threads upstairs. It would appear to me that the implematation of VST 3 in sonar is somewhat lacking.

There are some insights from Craig Anderton on why this may be in the main forum threads.

And Sample Tank 3 VST2 worls perfectly in X3

Working with 3.0.2 over the weekend and can confirm that VST3 is still a non-starter but VST2 works a treat!

I find myself opting for the vst2 versions of most plugs in Sonar due to issues with a few vst3 products. ST3 works well as vst2

It is just too CPU hungry for me. I can run pretty much anything I want in the way of VSTis in my projects. I put in the demo piano in ST3 and my CPU almost jumped out of the machine! Clicks, pops, moans, groans! No ST3 for me.

Skyline_UK
I raised a ticket to iK Support when ST3 was released to tell them the VST3 version was duff. That was over a month ago so I sent a reminder today. No reply yet. Apparently they didn't beta test with Sonar...
Use the VST2 dll and you should be ok.

I suspect that is because they haven't had enough complaints. If everybody logged a ticket to iK, and pointed them to this thread, I suspect they would be onto it pretty quick...

As I still had no reply to my IK ticket I posted yesterday on the IK forum. Peter, the IK guy there who always replies very quickly to issues raised (though most often saying you need to refer the matter to Support...) said he would take it up with them and get my ticket replied to. We'll see what transpires.