I just installed Tekemachus on my KSp 0.25, and when I use the "Open link"-button in KSP or open the link myself in my browser, i get only one message:
"Request Entity Too Large 414"
What did I do wrong?

I cannot recreate this issue on my development machine, so may I ask what browser and operating system you are using?

I'm running Chrome 38.0.2125.122 (64-bit) on Ubuntu 14.04.

After deleting all cookies for 127.0.0.1 and localhost, the problem disappeared...

Telemachus will return that error if the HTTP request is over 8000 bytes in length, so I guess the cookie data pushed it over that limit. There is currently no way to configure this value, but I will leave this issue open so that I remember to do this!

I have added a configuration option which allows the maximum HTTP request length to be adjusted, also, the default has been increased to 10000 bytes.