If you performed a custom installation and did not install the LDAP driver on the Identity Manager server, you have two options:
Install the files on the Identity Manager server, using the instructions in Considerations for Installing Drivers with the Identity Manager Engine
in the NetIQ Identity Manager Setup Guide
Install the Remote Loader (required to run the driver on a non-Identity Manager server) and the driver files on a non-Identity Manager server where you want to run the driver. See Configuring the Remote Loader and Drivers in the NetIQ Identity Manager Setup Guide.