Don't know what has happened. I opened an old project from back in May, and everything seems to work as usual until I try to record. Sonar goes through the motions and even shows the waveform as I record. But when I stop recording the waveform is not wrote to the channel. There is no information at all. I am completely stumped, but am convinced that its probably something simple, I just can't find the problem. Anyone have any ideas?

It may be a per-project setting in Preferences > Project > Record "Allow Arm Changes During Playback/Record" is set. Try deselecting it. Since it is a per-project setting, you may want to make sure the project templates you use are also configured correctly, to avoid this in future projects.