"ClassFactory cannot supply requested class" when starting map service with SOE or SOI enabled

Error Message

Attempting to start a map service after adding a Server Object Extension (SOE) or Server Object Interceptor (SOI) returns an error:

Error:   
ClassFactory cannot supply requested class

Cause

There are several possible causes for this error.

• The .NET Extension Support feature is not installed during the ArcGIS Server installation.
• The .NET Framework is outdated.
• Some references or custom codes are added to the SOE or SOI, or are using third party customizations. Missing DLLs may occur in some customizations where the user is required to insert the code manually.
   

Solution or Workaround

• Rerun the ArcGIS Server installation and install .NET Extension Support to enable all SOE functions in ArcGIS Server. .NET Extension Support allows ArcGIS Server to extend its capabilities with Server Object Extension (SOE) and Server Object Interceptors (SOI).

• Update the .NET Framework to the latest version, according to the ArcGIS for Server software requirements. For more information, refer to the following web help document, ArcGIS for Server: Installation Guide.
• Ensure all DLLs are included in the customized SOE file.