Not sure if you are using the same user that created the db lookup to make the search. I was able to get the lookup table when I used the same user. However, when I use a user with fewer capabilities, I got the same problem.
I added the dbx_user role to the user who has to search with this db lookup and it worked. However, it will expose the "External Database" section to that user. I'm still finding ways to avoid this while letting that user use the db lookup.
