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:
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Windows PowerShell is affected by the same issue as MMC.
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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: