It looks like a programming error on the part of TurboTax. Happened to me, too. I looked at the error report which had an image of the worksheet and noted that the worksheet had four columns for withholding payments in 2020 when there should only be three periods. I suspect that you filled out the information for Form 2210 before the 2/26/21 TurboTax update. If you did, you provided information for four periods. After the update TurboTax combined the first two periods into one period, but it appears that TurboTax left a "ghost" of you previous second period input in the worksheet and, presto, when they add all four columns in the worksheet it produces an error. I fixed it by zeroing out the 2nd column in the worksheet in the error report.
While that solved that error, TurboTax is currently not filling out Part IV of Form 2210 correctly. I will solve that by switching to the H&R Block tax software next year. This type of error is inexcusable two months into the tax season.
TurboTax is aware of errors related to calculating underpayment penalties on Form 2210. The problem has been reported and is under investigation. Taxpayers can continue to efile with the option of deleting the form and allowing the IRS to calculate any underpayment penalty for you.
How to delete a form in TurboTax CD/Download software
How to delete a form in TurboTax Online
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