I wasn't able to find much--there's only so much debugging you can do with a .bin file--but I did find something.
The first problem was the format of the filename. "Nightmare.x86_64" is a ".x86_64" file, which doesn't exist. When I renamed it to "Nightmare_x86_64(.bin)" I got this:
"no boot config - using default values
(Filename: Line: 474)"
On another note, both "LinuxPlayer_s.debug" and renamed "LinuxPlayer_s_debug" give the same error message:
"bash: ./LinuxPlayer_s.debug: cannot execute binary file: Exec format error"