ActiveSync users cannot synchronize an EAS device for the first time in an Exchange Server 2010 or Exchange Server 2013 environment

By Joseph Piggee Sr.
You can work around this , just assign the Exchange Servers group the right to change permissions against msExchActiveSyncDevices objects.
To do this, follow these steps:
1. Start Active Directory Users and Computers.
2. Click View, and then click to enable Advanced Features.
3. Right-click the object where you want to change the Exchange Server permissions, and then click Properties.
4. On the Security tab, click Advanced.
5. Click Add, type Exchange Servers, and then click OK.
6. In the Apply to box, click Descendant msExchActiveSyncDevices objects.
7. Under Permissions, click to enable Modify Permissions.
8. Click OK three times.
http://support.microsoft.com/kb/2579075