Third-party transport agents cannot be loaded correctly in Exchange Server 2013 SP1

Depois de noticiados alguns problemas com a instalação do Service Pack 1 do Exchange Server 2013, tal como o descrito no título deste post, a Microsoft disponibilizou um fix (KB2938053):

• Third-party transport agents cannot be loaded correctly in Exchange Server 2013 SP1

Brief Description
Describes an issue in which the Exchange Transport service cannot start in Exchange Server 2013. This issue occurs when third-party transport agents do not load correctly.

Overview
After you install Microsoft Exchange Server 2013 Service Pack 1 (SP1) or you upgrade an existing Microsoft Exchange Server 2013 installation to Exchange Server 2013 SP1, third-party or custom-developed transport agents cannot be installed correctly. Additionally, the Microsoft Exchange Transport service (MSExchangeTransport.exe) cannot start automatically. Specifically, you cannot enable third-party products that rely on transport agents. For example, you cannot enable anti-malware software or custom-developed transport agents. When the installation fails, you also receive an error message that resembles the following: The TransportAgentFactory type must be the Microsoft .NET class type of the transport agent factory.