While this likely does not address the issue posed by jclusen this may fix issues other individuals encounter with this error.
I needed to change data that I had entered in the Step-by-Step mode. In particular I needed to delete extra data associated with health care data involved with multiple 1099-HCs. It would not let me change it using that mode, so I went to Forms view and modified it there. The changes worked and I was able to save the data. The next time I started up Turbo Tax it generated the error 25300 and it defaulted to Forms view. Since those changes were the last activity I had done, I went to the data in Forms view and deleted the data as well as other data in that form. However, just deleting the data I had changed might have been enough. Anyway, I saved my tax data and exited. When I opened the taxes again, my taxes opened successfully in Step-by-Step mode. So now I was able to add the data correctly using Step-by-Step mode.
I've noticed in past years issues you have to be careful entering data in Step-by-Step mode and then modifying it in Forms view.
