It doesn't like the umlaut in "fnf".  You have to tell Ruby that this script file (the actual text file, with your ruby source code in) is encoded in something other than US-ASCII.

Try adding this comment as the first line in your script file:


# encoding: UTF-8


That way, as soon as the Ruby parser opens the file, it knows to interpret "fnf" as four UTF-8 characters, rather than five raw octets ("\x66\xC3\xBC\x6E\x66"), two of which aren't valid 7-bit US-ASCII.

Google "ruby magic encoding comment" for further reading.