I clicked save to save my project last night and got the same message. I kept clicking save and it finally saved. I have plenty of hard drive space. Hasn't happened since. Sonar also closed in the middle of playback. No error message just completely closed. I've been having a lot of crashes. I'm running the current update. It always seems one thing is fixed and another broken. Once I find a stable version I'm not updating anymore. So much for paying for lifetime updates.
I love Sonar but the stupid little things that should always work cause a lot of down time. Since there is no more support I hope to find that stable update soon. It's just not worth the chance of an update screwing everything up. I guess I can take the chance and update every 6 months. I don't know.