An exception is returned while opening a template in the Exchange Toolbox

Symptoms

When you open a template in the Details Template Editor of the Microsoft Exchange Toolbox, it returns the following exception message:

"Microsoft.Exchange.Diagnostics.BlockedDeserializeTypeException: Deserialization of type System.Text.CodePageEncoding blocked due to NotInAllow at location SerializationTypeConverter."

This exception prevents you from editing the Details - Templates.

Additionally, you can’t use Windows PowerShell (PS) as a substitute for Microsoft Management Console (MMC) because of the following reasons:

• Windows PowerShell is affected by the same issue as MMC.
• The binary blobs that are returned for Details Template objects can't be edited in Windows PowerShell.

Resolution

To fix this issue, install the following security update:

• Description of the security update for Microsoft Exchange Server 2019, 2016, and 2013: March 14, 2023 (KB5024296)