The ldap.ora file (required to point to the server which holds all the connection details) is located on a network drive and a TNS_ADMIN string has been added to the Oracle Home details in the registry to point to this location. In the Server Login Window the LDAP Editor has a green check against it and when this is opened it's pointing to the correct location. However, when trying to connect using the LDAP tab in the Server Login Window the dropdown list of descriptors is not being populated. It is possible, however, to connect to a particular database if the descriptor is known.
Add a TNS_ADMIN environment variable to point to the alternative location i.e.
1. <Right Click> My Computer
2. Click Properties | Advanced | Environment Variables
3. Under 'System Variables' click 'New'
4. Set 'Variable Name' to 'TNS_ADMIN'
5. Set 'Variable Value' to the location of ldap.ora | OK
Place the ldap.ora locally in the %Oracle Home%\Network\Admin folder
If using an instant client, verify ORALDAPCLNTxx.DLL exists under client folder. The LDAP Descriptor will not be populated. Enter the database name in the Database field.
Waiting for fix in future release of Toad for Oracle