Error "1051429 Unable to Externalize users to Hyperion Shared Services" when Trying to Externalize Essbase to Shared Services

Getting Error "1051429 Unable to Externalize users to Hyperion Shared Services" when trying to externalize Essbase to Shared Services.
Also getting error "1051429 Analytical Services Product Existence Check Fails against the Shared Services Server with Error [Unable to Authenticate.]
Fatal Error: CSS Initialization Fails".
Both errors appear in the Essbase server log file.

Cause
The probable causes for the Essbase Error 1051429 are:

a. When externalizing the Essbase users to Shared Services or if Essbase users have been externalized successfully but could not be authenticated.
b. Changes in settings of Essbase Configuration file (essbase.cfg) or Essbase security file (essbase.sec).
c. Insufficient privileges or Credentials for the user Admin.
d. Unable to login into Shared Services due to invalid username or password.
e. Unable to login into AAS due to invalid username or password.

Solution
1. Identify if there are duplicate entries in Essbase.cfg file as below (note uncommented duplicate entries for AuthenticationModule):
The following entry specifies the full path to JVM.DLL
JvmModuleLocation /hyperion/common/JRE/Sun/1.5.0/lib/i386/server/libjvm.so
; SharedServicesLocation server_name 58080
; AuthenticationModule CSS http://server_name: 58080/interop/framework/getCSSConfigFile
; SharedServicesLocation server_name 58080
; AuthenticationModule CSS http://server_name: 58080/interop/framework/getCSSConfigFile
SharedServicesLocation server_name 58080
AuthenticationModule CSS http://server_name: 58080/interop/framework/getCSSConfigFile
SharedServicesLocation server_name 58080
AuthenticationModule CSS http://server_name: 58080/interop/framework/getCSSConfigFile
2. Take backups of the Essbase.cfg and Essbase.sec files.
3. Delete the duplicate entries in Essbase.cfg file.
; The following entry specifies the full path to JVM.DLL
JvmModuleLocation /hyperion/common/JRE/Sun/1.5.0/lib/i386/server/libjvm.so
SharedServicesLocation server_name 58080
AuthenticationModule CSS http://server_name: 58080/interop/framework/getCSSConfigFile
CssSyncLevel AUTO
4. Restart the Hyperion Services.
5. Login into Shared Services, and perform a Sync Native Directory.
6. Login into the AAS Console and then externalize all users to Shared Services.