You need to go to Active Directory, under Active Directory Users and Computers and give the farm account special permission, in this case it seems Network Service Account which user synchronization service is using.
- Go to domain, right click and select delegate control
- Click next and your UPSS account, click next
- Create custom task and click next, keep the default scope of the
task, click next
- Select the permission General and select replicating Directory
Changes,click next and finished.
After that add the account under local Security Policy to allow log on using log on locally option. Also you need to add UPSS account to local machine as admin.
Reboot your server.
- Now go to UPSS and enter your password and confirm password. It will
get started (wait for 5 mins)
Also you have to configure Synchronization connection and setting.