I have a reverb bus that's worked without problems on this project for a couple of weeks. All of a sudden, today, it just stopped working. Nothing going in or coming out. All of the sends are correctly routed there, and the bus has the master bus as it's output, but nothing happening. 

In the end I had to restart Sonar to get it working again. 

Now it's happened again, and restarting hasn't solved the problem. I basically have a dead bus. Any ideas?

Ha, well what do you know....I had a Guitar Rig reverb in the FX bin and for some reason the wet control has reverted to zero all by itself. This isn't the first time I've had problems with Native Instruments volume controls turning to zero of their own accord. It happened on a synth I was working on a few weeks ago - every time I hit play in Sonar, this synth would reduce it's volume to zero. No automation going on, nothing. I'm starting to feel there's shenanigans going on between Sonar and NI stuff.