When attempting to add a new server to server group the following error is encountered : 

An error occurred running the command: 'New-DeliveryServicesCertificate' The process does not possess the 'SeSecurityPrivilege' privilege which is required for this operation. At C:\Program Files\Citrix\Receiver StoreFront\Management\Cmdlets\UtilsModule.psm1:340 char:20 + $certificate = New-DSCertificate -X500 $certificateSubject ` 

1. Firewall should be disabled ( Disable the firewall profile with command : netsh advf set allp state off )
2. Change Cluster service account to local on both StoreFront servers.
3. Change the replication service account to local system.
4. Remove folder C:\ProgramData\Microsoft\Crypto\RSA\MachineKeys.
5. Add the Local Administrators group as a member of the manage audit and security logs in GPO (computer configuration > windows settings > security settings > local policies > user right assignments)
6. Ensure NT SERVICE\CitrixConfigurationReplication and NT SERVICE\CitrixClusterService are part of  local administrators group.If not then add it manually.
7.If the Cluster service is missing then, use the installutil.exe to install the service instance as follows :

Go to the path C:\Windows\Microsoft.NET\Framework64\v4.0.30319  and installutil.exe with the following path "C:\Program Files\Citrix\Receiver StoreFront\Services\ClusterService\Citrix.DeliveryServices.ClusterService.ServiceHost.exe"

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Problem Cause

1. Services instances are not present 
2. The local administrator does not have appropriate group membership

An error occurred running the command: 'New-DeliveryServicesCertificate' The process does not possess the 'SeSecurityPrivilege' privilege which is required for this operation. At C:\Program Files\Citrix\Receiver StoreFront\Management\Cmdlets\UtilsModule.psm1:340 char:20 + $certificate = New-DSCertificate -X500 $certificateSubject ` 

https://docs.citrix.com/en-us/storefront/3/sf-install-standard/dws-deploy-join.html