If you've mistakenly created a custom legend file for a project you can revert back to using the default legend file (you must also do this before you can use another project's custom legend file with a project that already uses a custom legend file).
To use the default legend file with a project that has a custom legend file:
- Open the project.
- Choose Legend > Revert to the Default Legend. (If this option isn't available then the project is either already using the default legend file, or you've opened the project in read-only mode.)