From what I have found there are no real error logs in lua, just what it prints out to the chat window, as for debugging you can try to use LuaEdit (
http://luaedit.luaforge.net/) but it didnt work out for me, maybe since I run windows 7, not sure. But it has a syntax checker option that should bring up an error if you have a bug that prevents LOTRO from loading the pluging (such as saying "unable to load plugin" without any other explination)
as for it not being able to find the file did you make sure the capitals were the same between your files? Lua is case spacific (found that out after a really annoying bug myself)