[Resolved] Newbie problem with external VSTs

I have X2 Producer 64bit and a Focusrite 18i20 interface.  I get clean sound when using any soft synths that came with producer.  However, if I use any external VST, i get serious distortion.  The distortion increases exponentially with the number of notes played simultaneously.  This didn't happen when I initially installed these VSTs, so I probably did or changed something.  As a newbie, I have no idea where to start looking.
 
Any suggestions would be appreciated.

You could try turning down the gain nob some. If you turn down the gain nob on the track and your problem goes away, clipping might be the issue.

hmmm. I definitely don't have this problem... so.. how would I trouble shoot?
 
If you route the signal you plan to send to the VST to a bus, you can check the level on the input to the bus..
route that bus to another bus and put the VST on it.
 
What VST are we talking about? All non-Sonar VSTs?
 
We need some path through which we can try to isolate the issue.
 
I suppose it's isolated if you click the power button on the effect -- turning it off -- and the distortion goes away -- click the power button -- distortion returns. Right?

As gswitz said, definitely check your drivers under "Edit" > "Preferences" > "Playback and Recording" > "Driver Mode", and make sure you are using ASIO. Also check your soundcard setup. I came back to Sonar recently and had distortion on VSTs, and this was the cause. Sonar defaulted to WDM. I was surprised to hear distortion because of this, I would have expected latency or dropouts.

Open up the MixControl panel (the driver controller for your FocusRite) and check the buffer size...if you are really only using 32 samples that might be the problem, although I would expect much smaller latency. I have a much less powerful (on paper) computer than you Core Duo 3GHz with 4GB RAM, and I use the 512 sample buffer setting...getting ~25msec round-trip latency. 
 
In the panel, pull down <Settings> and look for <Latency> (set to Medium) and <Buffer size> (set to 256 or 512). These should be 'safe' settings with tolerable performance. 
 
I have a Saffire PRO 40 and it is pretty touchy about the 'sweet spot'
 
Also, when I upgraded to X3, it didn't copy my settings perfectly from X1 (set drivers to WDM), and I had some problems before some nice person here on the forum pointed it out;...funny that I actually fell into the old habit of hitting the Wave Profiler button, without realizing that this is NOT an ASIO function....duuuhhhhh

without over analyzing or overthinking a possible cause, for sure its an easy test to set your ASIO buffer size to 256 or 512 samples to see if it goes away.. I don't know many systems with rock solid performance across the board at 32 samples.

If i know what synths you are using i can run some checks and see if i can replicate the problem. More info=better and faster solutions.

Are you sure you're running the latest drivers for your card? 32 samples giving you 45msec of latency at 44.1KHz should be an impossible combination of figures no matter what else is going on. And 512 samples seems a bit excessive for a decently specced system like yours.