Listener supports no services - tried everything, listener won't work

Hi all ... this is baffling. I'm running 11g on a virtual windows 2008 server, and it's a clone of a working system. Whatever I try I get "ORA-12514: TNS:listener does not currently know of service requested in connect descriptor" when I try to connect via a listener (it works fine if I connect while avoiding the listener).

The weird thing is that I had this same problem on the original machine before I cloned this, and fixed it. But I can't remember what I did to fix it, it might have been putting a SID list in the listener.ora file, it might have been changing the order of elements in the PATH variable, it might have been eye of newt and toe of frog for all I know, it's a baffling and bewildering maze of permutations of things that I've tried.