Well, Peter, I’m affraid that this has nothing to do with the theme.

> The server encountered an internal error or misconfiguration […]

I know absolute nada about server configuration. Just a wild guess: If the server runs the most recent version of PHP (5.6 as far as I know) and there are some “knots” in the themes source code that is not compatible with that …?

My only surgestion:

> Please contact the server administrator and inform them of the time the
> error occurred, and the actions you performed just before this error.