This is a file that I have been importing to AI successfully for several years. It only failed after I upgraded to AI 9.0B. As suggested, I did a sample export and saw the problem right away. The first field that AI 9.0B exported was IN, indicating the Header Type. My import file has I in the Header Type field, a change that I had failed to notice. I assume that it will work after this change. I will be at the client's office tomorrow and will test.

Thanks.