I was also testing newrelic, but I fail the same way Lars does.
I am now told by the community moderator that Plugins are not supported for EU, which means that the Domino Interface to NewRelic does not work for EU - in my case and judging from the name in Lars's case also - germany.
Here is a doc mentioning that:
Well there should be other services... :(
Hopefully this info helps some people save some time.