configure f5 login using AD

For what? The Bind operation, or as the user to log on to the BIG-IP with? If the former, try setting Scope to Base. Otherwise, you need just enough permissions on the Bind account to perform a query.

In any case, try watching the LDAP traffic with a WireShark capture. LDAP is pretty verbose about its errors, so you should see what's going on inside the capture.