your search settings are not returning any results, it usually means your Base DN is wrong, or you just fudged up the search string.
Create a new connector, and set the minimal number of entries to make sure it connects - you can test things with the excellent softerra LDAP Browser, which will show you what the connector can see.
This is going to be my homepage for the next few weeks!!!
an oversight in the DN
the simple things are always the most unobvious.