@lchriste
The IRS calls any error in a tax return a calculation error. It doesn't necessarily mean that the calculations were wrong. Most of the time the error is caused by incorrect or missing input. The TurboTax calculations were correct for the input that was provided.
When the IRS says that Social Security income was calculated incorrectly, it's usually because they corrected some other income on the tax return. Did they change anything else besides your Social Security income? A change in any other income will change the amount of your Social Security that is taxable. One other possibility is an incorrect answer to the question about whether you or your spouse live in certain foreign countries. This question is new this year, and some people have misread it and answered incorrectly. See the discussion about this new question at the beginning of this thread, above your post.
TurboTax will reimburse you for penalties or interest that you had to pay because of an error in the TurboTax calculations. You can submit a claim under the Accurate Calculation Guarantee.
You probably do not have to correct your tax return. If the IRS reduced your refund they have already made the correction. You do not have to do anything unless the IRS notice tells you to correct it.
