Activesync error InvalidSyncKey

Trying to get iPhones working for one of our customers. SBS 2003 SP2, Exchange V6.5 SP2. OWA is working correctly. Verified all of the settings we normally need to modify in a SBS2003 Activesync scenario. Getting the following error from testexchangeconnectivity.com:

 An ActiveSync session is being attempted with the server. 
  Errors were encountered while testing the Exchange ActiveSync session. 
   Test Steps 
   Attempting to send the OPTIONS command to the server. 
  The OPTIONS response was successfully received and is valid. 
   Additional Details 
  Headers received: MicrosoftOfficeWebServer: 5.0_Pub
Pragma: no-cache
Public: OPTIONS, POST
Allow: OPTIONS, POST
MS-Server-ActiveSync: 6.5.7638.1
MS-ASProtocolVersions: 1.0,2.0,2.1,2.5
MS-ASProtocolCommands: Sync,SendMail,SmartForward,SmartReply,GetAttachment,GetHierarchy,CreateCollection,DeleteCollection,MoveCollection,FolderSync,FolderCreate,FolderDelete,FolderUpdate,MoveItems,GetItemEstimate,MeetingResponse,ResolveRecipients,ValidateCert,Provision,Search,Notify,Ping
Content-Length: 0
Date: Fri, 11 Feb 2011 19:54:32 GMT
Server: Microsoft-IIS/6.0
X-Powered-By: ASP.NET

 Attempting the FolderSync command on the Exchange ActiveSync session. 
  The FolderSync command completed successfully. 
   Additional Details 
  Number of folders: 11 
 
 Attempting the initial sync to the Inbox folder. This initial sync won't return any data. 
  The Sync command completed successfully. 
   Additional Details 
  Status: 1 
 
 Attempting to test the GetItemEstimate command for the Inbox folder. 
  ExRCA received an error in response to the GetItemEstimate command. 
   Additional Details 
  Exchange ActiveSync command GetItemEstimate failed with error code InvalidSyncKey. 

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