Assume that you are using an Exchange Web Service (EWS) based application in a Microsoft Exchange Server 2010 environment. In this situation, you cannot access mailboxes, and you receive a "503 Service Unavailable" error. Additionally, the following events are logged in the Application log on the Exchange Server 2010 Client Access server:

Log Name:      Application
Source:        MSExchange Common
Date: Date
Event ID:      4999
Task Category: General
Level:         Error
Keywords:      Classic
User:          N/A
Computer: Computer
Watson report about to be sent for process id: Process ID, with parameters: E12, Build Type, Version Number, WS, System.Web, S.W.U.WebServiceParser.GetCompiledType, System.InvalidCastException, XXXX, Version Number.
ErrorReportingEnabled: True

Log Name:      Application
Source:        ASP.NET 2.0.50727.0
Date: Date
Event ID:      1309
Task Category: Web Event
Level:         Warning
Keywords:      Classic
User:          N/A
Computer: Computer
Event code: 3005
Event message: An unhandled exception has occurred.
Event time: Time 
Event time (UTC): Time 
Event ID: ID 
Event sequence: XXX 
Event occurrence: XX
Event detail code: 0

Application information:
  Application domain: /LM/W3SVC/1/ROOT/EWS-1-XXXXX 
  Trust level: Full
  Application Virtual Path: /EWS 
  Application Path: Drive:\Program Files\Microsoft\Exchange Server\ClientAccess\exchweb\EWS\ 
  Machine name: Computer 

Process information:
  Process ID: Process ID 
  Process name: w3wp.exe 
  Account name: NT AUTHORITY\SYSTEM 

Exception information:
  Exception type: InvalidCastException 
  Exception message: Unable to cast object of type 'System.Web.Compilation.BuildResultCustomString' to type 'System.Web.Compilation.BuildResultCompiledType'. 

Request information:
  Request URL: URL
  Request path: /EWS/Exchange.asmx 
  User host address: IP 
  User: User 
  Is authenticated: True 
  Authentication Type: NTLM 
  Thread account name: NT AUTHORITY\SYSTEM 
Thread information:
  Thread ID: Thread ID 
  Thread account name: NT AUTHORITY\SYSTEM 
  Is impersonating: False 
  Stack trace: at System.Web.UI.WebServiceParser.GetCompiledType(String inputFile, HttpContext context)
   at System.Web.Services.Protocols.WebServiceHandlerFactory.GetHandler(HttpContext context, String verb, String url, String filePath)
   at System.Web.HttpApplication.MaterializeHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)


This issue occurs because the Exchange server does not use a correct handler to process the EWS request.


To resolve this issue, install the following update rollup:

2785908 Description of Update Rollup 5 version 2 for Exchange Server 2010 Service Pack 2


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

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