You may have significant qualifying dividends and/or net long-term capital gains (e.g., over $50,000). There would be a qualifying dividend and capital gain worksheet that you can see in forms mode.
one other possibility if you are 90 or older and used the alternative tax computation on lump sum distributions (Form 4972).
This forum has no access to your return, so if this doesn't resolve your issue, you'll have to contact support.
