Answered
I read one of the forum threads with same problem. The difference is, I'm combing 4 Illustrator CS5 documents, which of course get distilled when combined. But on saving I get the same error message. They are very simple in structure and content and each has a small lo-res image embedded.
I've also tried saving each as a pdf first then combing with the same error.
I combine files with more pages and large embedded images frequently and have never encountered this one.
Help anyone?