as it's all done server side, it could be any number of things which has caused it, even an issue on metrolyrics side themselves.
trying it out myself (never used it before so not sure what is / isn't normal) i see the same error response in Winamp. clicking the 'more' link i get the following:
Service name: MetroLyrics
Error code: 0x800C0005
Was Made For Lovin' You
Service id: 222151
trying that url in a browser gives the same response. however removing the 'daan.' part then provides a page with lyrics on it. so i'd have to go with metrolyrics having changed something purposefully on their end or it's a known server issue.
as such, Winamp's handling is correct for how online services are meant to work (since the view is just hosting whatever the service does off it's own servers). best to send them a message via http://www.metrolyrics.com/contactus.html