[Theme: Hemingway] 500 Errors on page call

WordPress 3.6
Hemingway 2.5.7
(the DL url is https://warpspire.com/hemingway/ …. yes, the theme is OLD OLD OLD)

Version: 2.5.7
Hemingway is a simple weblog theme by Kyle Neath aimed at giving bloggers a great platform on which to customize. This is a WordPress 2.5/2.6 port by Xiaoka.

Whenever I go to the menu at the bottom of any page, and click on another page (say, https://www.url.com/about) I get this error message:

The website encountered an error while retrieving https://www.URL.com/about/. It may be down for maintenance or configured incorrectly.
Error code: 500

I also note that I cannot get to the pages from the ALL PAGES page, and not from the VIEW PAGE button when editing the page itself.

When I change themes – everything comes back on line and functions spiffy.

Any general ideas of what’s up?
I am guessing it is something about the way the theme is parsing the information that constitutes the page name and renders the appropriate URL.. but how exactly that functions – is waaaay beyond me.

Conversely – does anyone know of a theme that looks A LOT like this and is being currently maintained? I’ve looked, but no luck so far.