If your Exchange Organization has multiple Exchange Servers with the Client Access Role (CAS) with different Exchange versions, then after an upgrade on any of the CAS servers to Exchange 2010 SP2 with RU1 or RU2 or RU3 you may have a problems with CAS to CAS proxying.

The 2 events that might be logged in event viewer: event ID 136 and Event ID 4999:


Event ID: 136

Log Name: Application

Source: MSExchange OWA

Task Category: Proxy

Level: Error


The sign-in to Outlook Web App failed. User /o=xxxx/ou=xxx/cn=Recipients/cn=user has a mailbox on server version. However, no Client Access server or front-end server with a matching version was found to handle the request.

For users on Exchange 2007 and above, you can configure the Outlook Web Access URL for redirection using the externalURLparameter on the Exchange /owa virtual directory.


Event ID: 4999

Log Name: Application

Source: MSExchange Common

Task Category: General

Level: Error

Description: Watson report about to be sent for process id: 744, with parameters: E12, c-RTL-AMD64, 14.02.0247.002, OWA, M.E.Clients.Owa, M.E.C.O.C.ProxyUtilities.UpdateProxyUserContextIdFromResponse, M.E.C.O.Core.OwaAsyncOperationException, 413, 14.02.0247.002.



Exchange 2010 SP2 RU1 package introduced a change to the user context cookie which is used in CAS to CAS proxying. This issue causes a temporary incompatibility between SP2 RU1 or RU2 or RU3 servers and servers running earlier versions of Exchange. The change is such that earlier versions of Exchange do not understand the newer cookie used by the SP2 RUx server.

Below is a table showing Exchange server version compatibility in CAS proxying.

You will need to update any server that does not have any rollup installed.

[table caption=”” width=”500″ colwidth=”20|100|50″ colalign=”left|left|center|left|right”]
Server proxy,Server being proxied to,Solution
Exchange 2010 SP2 RU1,Any version of Exchange 2010 older than SP2 RU1 ,Apply Exchange 2010 SP2 RU2
Exchange 2010 SP2 RU1,Exchange 2007, Apply Exchange 2007 SP3 RU7

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