The original link: http://www.cnblogs.com/myyouthlife/p/3284291.html

Problem description:
An error message appears when the deployed SOE is enabled for a service. If the newly deployed SOE is enabled for SampleWorldCities, the error message is as follows:
service failed to start
SampleWorldCities.MapServer:

ClassFactory cannot supply requested class
 
Causes:
This error message usually appears in.NET SOE because.NET extension support was not enabled when ArcGIS Server was installed.
Solutions:
Fix arcGIS Server, enable.NET support. The screenshot below

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Update 9.29 days
In addition to the above, there is another situation in which the arcobjects SDK that is adopted by the opening of SOE is issued with the wrong version and the arcobjects SDK that is owned on the deployment machine. For example, the ARcobjects SDK for.NET 10.2 is adopted for soe development and deployed on a 10.1 Server machine, and only the Arcobjects SDK for.NET 10.1 is on the machine. The above error will also occur