Your document (e.g., "filename.fadein") was created using an earlier version of Fade In.

When a new major version of the software is released, the version of documents saved with it will match the new software version. Updating the document allows you to keep a backup of the copy in the previous version, if you so choose to.

(Fade In is always able to open previous-version documents without issue.)

You can always simply choose to re-save your document under the original name (i.e., saving "filename-updated.fadein" as the original name "filename.fadein").