Exchange users cannot access email on smartphone - Security Permissions error

source: http://support.microsoft.com/kb/2579075

To work around this issue, 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.
   I did this on the select users that needed access to ActiveSync and it worked. I tried it first on the Domain and it appears to not have worked and inheritance is enabled?!?
   Note You can change permissions against a user, an organizational unit, or a domain.
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. Don't worry about the 'Descendant' part, just use msExchActiveSyncDevices
7. Under Permissions, click to enable Modify Permissions.
8. Click OK three times.

source: http://support.microsoft.com/kb/2579075