Exchange Event id 3 WebHost failed to process a request

Jeżeli macie problem z uruchomieniem serwisu Microsoft Exchange Mail Submission  lub Microsfot Exchange Transport lub jeżeli użytkownicy nie mogą usunąć wiadomości korzystając z OWA (Microsoft Outlook Web Access) otrzymując komunikat:
An unexpected error occurred and your request couldn’t be handled

sprawdźcie Event Log i poszukajcie poniższych błędów:

Event ID: 3 
Description:
WebHost failed to process a request.

Event ID: 1031
Description:
The service configuration file could not be loaded for the following reason: System.Configuration.ConfigurationErrorsException: Configuration system failed to initialize —> System.Configuration.ConfigurationErrorsException: Unrecognized configuration section system.serviceModel. (C:\WINDOWS\Microsoft.NET\Framework64\v2.0.50727\Config\machine.config line 134) at System.Configuration.ConfigurationSchemaErrors.ThrowIfErrors(Boolean ignoreLocal)

Event ID: 1002
Description:
Unable to start the Microsoft Exchange Mail Submission service: System.Configuration.ConfigurationErrorsException: Configuration system failed to initialize —> System.Configuration.ConfigurationErrorsException: Unrecognized configuration section system.serviceModel. (C:\WINDOWS\Microsoft.NET\Framework64\v2.0.50727\Config\machine.config

Jeżeli znajdziecie takie wpisy oznacza to, że macie problemy powstałe po zainstalowniu KB2756920 .NET Framework Update.

Rozwiązaniem jest zainstalowanie: KB2637518 Hotfix for Microsoft .NET Framework 3.5.1 on Windows 7 RTM and Windows Server 2008 R2 RTM