http://blog.nick.mackechnie.co.nz/post/2009/11/20/Exchange-2010-Active-Sync-Issue.aspx
Hi All,
  I’ve spent the last few days 
migrating to Hyper-V, SQL 2008, Windows Server 2008 R2 and Exchange 2010
 from 3 machines - Windows Server 2003, SQL 2005 and Exchange 2003. The 
last thing I had to turn on/get going was Active-Sync for syncing mail 
with home via a mobile device. This failed miserably, as per the below 
event log on my Exchange 2010 Server.
  Log Name:      Application
  Source:        MSExchange ActiveSync
  Date:          11/20/2009 12:23:07 PM
  Event ID:      1053
  Task Category: Configuration
  Level:         Error
  Keywords:      Classic
  User:          N/A
  Computer:      <server>.thenet.gen.nz
  Description:
  Exchange
 ActiveSync doesn't have sufficient permissions to create the 
"CN=<name>,OU=<OU Name>,DC=thenet,DC=gen,DC=nz" container 
under Active Directory user "Active Directory operation failed on 
<server>.thenet.gen.nz. This error is not retriable. Additional 
information: Access is denied.
  Active directory response: 00000005: SecErr: DSID-031521D0, problem 4003 (INSUFF_ACCESS_RIGHTS), data 0
  ".
  Make
 sure the user has inherited permission granted to domain\Exchange 
Servers to allow List, Create child, Delete child of object type 
"msExchangeActiveSyncDevices" and doesn't have any deny permissions that
 block such operations.
  Details:%3
  Event Xml:
  <Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
    <System>
      <
rovider Name="MSExchange ActiveSync" />
      <EventID Qualifiers="49156">1053</EventID>
      <Level>2</Level>
      <Task>2</Task>
      <Keywords>0x80000000000000</Keywords>
      <TimeCreated SystemTime="2009-11-19T23:23:07.000000000Z" />
      <EventRecordID>9577</EventRecordID>
      <Channel>Application</Channel>
      <Computer><server>.thenet.gen.nz</Computer>
      <Security />
    </System>
    <EventData>
      <Data>CN=<name>,OU=<OU Name>,DC=thenet,DC=gen,DC=nz</Data>
     
 <Data>Active Directory operation failed on 
<server>.thenet.gen.nz. This error is not retriable. Additional 
information: Access is denied.
  Active directory response: 00000005: SecErr: DSID-031521D0, problem 4003 (INSUFF_ACCESS_RIGHTS), data 0
  </Data>
    </EventData>
  </Event>
  The
 work around was pretty simple, however took me some time trolling 
through external and internal Knowledge Base Articles. I came across 
this article, however it didn’t seem to address the issue. 
  Here’s how I managed to get it sorted - 
  On a Domain Controller, Click on Start/All Programs/Administrative Tools/Active Directory Users and Computers
  
 
  Click on View and Select Advanced Features
  Select a mailbox that isn’t working with Active Sync, double click on the account, Select the Security Tab and then the Advanced Button.
  
 
  Select Exchange Servers, and tick the Include inheritable permissions toggle then Apply and OK. 
  
 
  This issue is currently bugged and is likely to be fixed with an update in the future – It seems to be a symptom of ‘upgrading’.
  Nick.