@2manyyear- The error stems from a legacy utility being removed from Windows 11, which TurboTax Desktop previously to use to generate the unique machine id (UMID). We have already updated TurboTax to remove the code that used the removed utility. However, if you installed TurboTax before it was updated (and after the legacy utility was removed), then the proper UMID was not associated with the license. Changing the TTConfig.ini file forces the software to use whatever was used in place of the UMID. 

If you don't see a UMID file , then please contact our phone support team for more assistance. 

Thank you TurboTaxSusan.  While you were replying, I kept working on the issue, and eventually manage to find the files that I  needed to modify.  I have added some clarification to my original post, to help others.

Your explanation is clear, and I am very glad to hear that TurboTax has solved it for future users. 

I routinely access past year Turbotax apps and files when doing current year taxes.   As with the majority of users, I have a new computer due to Windows 11 requirement.   I did add all of these past year TT apps to the new computer.   However, when I go to the Program Data folder mentioned higher in this post, I only have 2 years of subfolders, 2023 and 2025 (I've had TT desktop since 2020).   I need to run 2024 but the activation code doesn't work, and there is no TTconfig file to update the UMID.  How do I activate these past years of TT?

@bertible Are you getting an error code when you enter the License Code? Are you using the same login info as you did when you installed TurboTax on your old computer?