Why won't TurboTax Deluxe allow me to exclude the gain on a home that I had lived in for over two years, when I had never previously taken the capital gains exclusion?

This literally seems like a bug in TurboTax Deluxe.  I was a first-time homeowner who sold my first home after living in it for over two years.  I had a modest gain of under $10,000 but TurboTax keeps saying that my gain is taxable.