Hello All,
If your having such issue with an Exchange 2013 system, please make sure that you apply the Microsoft Patch prior to installing Avast, then we recommend installing a light installation on the Exchange server to include Antispam, Exchange and File system if you have, other options such as script, web, etc, should not be included to keep your Exchange server from having any complications.
You can find the Patch Below
http://www.microsoft.com/en-us/download/details.aspx?id=42065
Make sure that after the patch you have the following KB Fix below.
Exchange2013-KB2938053-FixIt.zip
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.
Thus the reason for the patch.
I hope this helps and if you have any further issue please contact us at absfeedback@avast.com for support.
Kind Regards
Che’ Johnson