Yes, it turns out that the game gives you a selection of letters, like Scrabble, to fill in all the text fields shown. You get the 500 error if you leave the text fields blank. It would be nice if the site gave a JavaScript alert instead of submitting the form with invalid input.

Unfortunately, that was a bug. If the number of characters you provided was less than the length of the word you gave, the server 500'd.

Oops! Sorry about that, the link should be fixed now!