Nav bar updates won't work, "page not available"

I am using Thesis version 1.8b, and I can’t tell if this is a theme issue or something else. I’ll also put it out there now that I only know the very basics of programming and don’t feel comfortable going into the source to try to determine/repair what’s wrong.

When I try to change my nav bar through the Thesis Site Options menu, I click “Save” and it takes a very long time to load, then it lands me on a “page not available” and my changes do not stick. Every time.

I did not build this page, I recently came on as a staff member at an organization that has had considerable turnover since setting the page up. I have access to our FTP but I don’t see where I can make the changes I need to make.

Since messing around with the nav bar, 3 rogue items have appeared that link to nothing. I deleted the pages since they have appeared, but that didn’t fix it.

Any suggestions? Our URL is https://edgewater.org