The error message suggests that there might be an issue with the .ftb file or the Family Tree Builder software. You can try the following solutions:
1. Make sure you have the latest version of Family Tree Builder installed.
2. Verify that the .ftb file is not corrupted or damaged.
3. Try opening the .ftb file on a different computer or reinstalling the software.
If the issue persists, you may need to reach out to MyHeritage support for further assistance.