American Opportunity Credit

TurboTax says I do not qualify for the American Opportunity Credit. I clicked on the "why didn't I get this?" button, which came up with the following:

"Not everyone qualifies for this credit. The most common reasons why you wouldn’t qualify for the American opportunity credit are:

  • Your enrollment status was less than half-time
  • You weren't enrolled in a degree program
  • You're under age 24 and don't support yourself. You're claimed as a dependent on another person's tax return, like your parents
  • You're filing as married filing separate
  • Your income is more than $90,000 ($180,000 if you file a joint return)"

None of these items apply to me. Why else might I not qualify for the credit?