This occurred & was discussed before, but I can't find those threads - might have beeen purged.
The error appears to be caused by code running on servers.
Below
404 Not Found you will see
nginx/1.6.0.
Read the following for clarification: (-; More at Reverse Proxy Server.
http://en.wikipedia.org/wiki/Nginx
After browsing a number of tech boards, it seems the program can run into a situation where ...
... blah, blah, blah ...
because a URL & a file name (thread-page) in a directory are the same.
Also, the last slash can cause problems.
In short, the server issues a redirect which loops until it times out & returns a 404 error.
Technically incorrect, but often the default.
I ran some tests with Bab's thread.
These don't work:
http://www.crosswordsolver.org/forum/430643/star?thread-page=
http://www.crosswordsolver.org/forum/430643/star
These do:
http://www.crosswordsolver.org/forum/430643/star/
http://www.crosswordsolver.org/forum/430643
so simply backspace in the address bar to get something like the last example.
I see Jazzgirl has already sussed this out. Well done !
Why Bab's threads are afflicted, & then Chrise's, I don't know. OS, browser, protocol interaction ...?
Too many variables.
All those protocols are like troops of chattering monkeys. How they manage to communicate at all is a miracle !