Nominatim search results are always empty

Question

On my Nominatim server, I'm trying to find something on a map. For example, I'm trying to find London on my map. I always got:

 No search results found
 Addresses and postcodes are approximate 

Can someone tell me how to fix this? Here are the links to the site and the xml results for something

  [1]: http://91.185.184.63/nominatim/search.php?q=London&viewbox=-151.18,66.02,151.18,-66.02
  [2]: http://91.185.184.63/nominatim/search?q=london&format=xml "XML Results"