日志文件显示我的自定义操作程序集无法正确加载。原因是我无意中删除了以下部分：

The log file shows my custom action assemblies could not be loaded properly. The reason is I have unintentionally removed the section:

<startup useLegacyV2RuntimeActivationPolicy="true">
<supportedRuntime version="v4.0" />
</startup>

从配置文件中。重新添加它，一切都可以正常工作。

from the config file. Added it back and everything works now.