Hi
This means there is no association in you browser between the link telnet:// and an application on your pc that can do telnet.
It is a link like http:// ssh:// or ftp://. it needs to be associated with an application.
If you google it, you will probably find a way to enable it for your favourite telnet application. You may even find it on this forum as I recal having seen examples for various telnet applications
Cheers,
Michel