Are you manually adding the ActiveSync account or trying to autodiscover? If autodiscover isn't configured then ActiveSync will fail. Try a manual mailbox setup just in case.
If you are trying manual and it is failing I would check to make sure both the domain and the user have activesync enabled. Also, try connecting from a different piece of kit just in case. Usually after enabling the ActiveSync license and enabling the domain/user for the mailbox it should work fine. We have Outlook 2013 with ActiveSync and it is working normally apart from sometimes it doesn't push emails even though they are in the mailbox.