Problem with Virtual Instruments and Recording Audio

I'm using an Audigy soundcard, a Variax going through a Guitar Port, and Sonar 4. The virtual instruments run great when they're by themselves, but Sonar drops out and locks up when I start Guitar Port to record audio. I've varied the sequence of starting the programs (1st sonar, then Guitar port and vice versa). I'm using WDM drivers, not ASIO.

Any ideas? Just the soundcard?