This error can occur after cloning an existing VIP Enterprise Gateway.
A VIP certificate is required to establish trust with the VIP Cloud. During the installation and initial connection to the VIP cloud, unique attributes are assigned to the Gateway using the established key pair. When a VIP Enterprise Gateway is 'cloned' and LDAP synchronization is attempted from the clone, the cloned data creates a collision condition in the VIP Cloud. This results in the failure "<<WARNING>> User Synchronization failed. Error: null,op=Synchronization".
Shut down the cloned server and discontinue use, then build a fresh VIP EG installation. From the source EG server, use the Export feature to transfer the configuration settings from the VIP Enterprise Gateway to the new server. Import the exported ZIP file into the fresh VIP EG server. (See: Exporting and importing configuration settings)