After I updated my computer to Windows 8.1 (from Windows 8.0), I got a garbled error message on my screen that said something about “Code D100” and PPPoE. I couldn’t read the rest of it because it was in incorrectly encoded Japanese, despite the fact that my computer is Japanese. I figured out that the problem was with the Flet’s Connection Tool (フレッツ接続ツール). I was able to fix it by downloading a new version of the connection tool.