Opening a Questionnaire or BidTable excel sheet outside of Bonfire prompts the user with an error message from Microsoft Excel:
This is often caused by a long file name and may present further issue if saved as a compressed filed (if you're downloading "all files" as a .zip).
Option 1: If the file presents as a "read only" document, click on "File", "Save As", and give your file a new name before hitting "Save". Save preferably in a different location so that there is no confusion between files and delete the original file.
Option 2: Rename the saved file to a shorter filename prior to saving it.