David,
I'm sorry you experience difficulties with Nisus Writer Express (though I notice that yuo've posted this in the "Pro" forum).
What you describe is quite odd.
The next time this occurs, please, when you notice that you cannot use the footnotes:
1. Choose Send Feedback from the Help menu inside Nisus Writer Express.
2. Describe what happened.
3. Please include the file in question.
4. Send in the report.
If we're lucky we'll get some information about what's happening inside your computer.
This report goes directly to the Engineering Department. I'll let you know as soon as there's anything meaningful to report.
In addition if you want to send a copy of the file to <
support@nisus.com> I'll check to see what I can learn as well.
Thank you for your patience.