When trying to create a new connection for the user profile synchronization service you may get this error :

‘Cannot navigate to the requested page while User Profile Synchronization is running. Please wait for the current Synchronization run to finish.’

One of the reason for this error is that the underlying service is hanging.

Go to Central Admin – > Application Management – > Manage Services on server

Make sure both user profile service and user profile synchronization service are both started.

You can also try to restart the timer job.