Users may notice errors with the built-in bandwidth test, which may be caused by a few things:
- You are using an outdated version of the Killer Control Center. Try clean installing the latest version by following the guide here – Clean Install The Killer Control Center.
- Sometimes the nearest server to you may be down, resulting in an error. This issue will usually clear itself quickly as either the server will come back up, or the service will reroute the request. In the meantime, you can use a service like http://www.speedtest.net to test your speed, then input the upload and download values manually. There is no disadvantage to setting your speeds this way.
- If you have an antivirus or firewall application, it may be blocking the speed test applet with an outgoing blocking rule. You may need to add an outgoing exception for the applet speedtest.exe in your antivirus or firewall application. You can find speedtest.exe in C:\Program Files\Killer Networking\Killer Control Center if you installed the Killer Control Center in the default location.