This error message came up after the previous error message about changing how box 12 is reported on the return.
TurboTax programmers are currently implementing some recent IRS changes for reporting SEP and SIMPLE plan contributions. While there isn't an estimated date when the changes will be done, you can test this by editing your W-2 every 5-7 days to check on the status.
On January 8, 2024, the IRS released a notice describing many changes required to implement the Secure Act 2.0. If you try to enter Code S for Box 12 of your W-2, you may see this message: "We're updating how SEP and simple plan contributions are reported on the tax return based on new guidance from the IRS."
Section 601 of the Secure Act 2.0 refers specifically to Simple and SEP Roth IRAs. Code S in box 12 defines how to handle a SIMPLE plan.
These last-minute IRS (and law) changes often cause implementation delays for TurboTax and other tax processors.
Please be patient while TurboTax works to understand all the ramifications of this IRS Notice then code and test the changes.