I installed CS about 2 weeks ago, and have seem this same save error situation several times in 2 weeks. I am running Mac 10.2.8. The files which have produced this error all have linked Photoshop format images placed in the layout. I have found that I can save the file if I am willing to sacrifice the linked images. I am able to copy the vector artwork and paste into a new file. As long as I skip the placed images, I am able to save the rest of the artwork into a new file. I can save this file into the same directory where I was unable to save the file previously.

Initially, I was working with files saved to a second drive, because my boot drive is not large enough to save all my Photoshop and illustrator files. This also means my boot drive didn't have a lot of spare space. I cloned my system to a larger drive, and copied the Illustrator master and the photoshop placed images to my Documents directory in my Home directory.

These steps seem to have cleared up my problem. I have a hunch that working with files in ~/documents was the important factor, but would also think it could have been corruption on that drive, or lack of free space for swap files. I don't really think it was the latter, but will need to do additional testing to know. For now, I seem to have solved the problem on my system.