Odd trouble with recording midi to audio

I've been working on a project that uses mostly soft synths, but also uses a K2600 for a Hammond sound. I had already recorded the k2600 midi to audio, then decided to add some extra bits. Once I was satisfied, I deleted the former recording, armed the track, soloed the midi, and started the recording off. Nothing would record. The Kurzweil was pumping happily away, Db meters showed input and all that. No audio squiggles to be seen. Tried echo on/echo off in various combinations to no avail. Tried switching audio driver from WDM to ASIO and back again. Rebooted the machine. Threw the I Ching. Finally I gave up (I am the furthest thing from a Sonar guru) and just created a new project with 1 midi and 1 audio track. Copied and pasted the midi from project 'real' to project 'temp', set up the midi in the temp project to point at the k2600 and recorded the audio there. Then I copied the audio, and pasted it back into the 'real' project and was good to go. I suspect I did something to make recording the audio impossible, but I haven't got the faintest clue what that might have been. The other possibility is a Sonar glitch I suppose, and I have hit a few of those, but my guess is Las Vegas would put the odds on 'user did something stupid'. And...just remembered this and its probably worth mentioning....It was nothing specific to the Kurzweil or its midi track. Tried audio recording other tracks with no luck either. Anyways....any guesses what this might be?