I have found the bug, by going back to the beginning and re-entering everything very carefully, and keeping copies of the tax return file as I went.
Everything is OK up to the federal return review. It finds an "error" on the "Tax & Int Wks". The box there asking if my mortgage interest [deduction] needs to be limited is checked "y", but this should be "n", according to the instructions there and in the appropriate IRS publications.
The lesson is that during reviews, check every question against the form it is asking about. Often these are in worksheets used to build up the final return, and in this case there is a logic bug someplace.
