IIS Error: The only key properties "fileExtension" is set to ".json", can not be added to type "mimeMap" a collection of duplicate items

When you open a asp.net mvc project using visual studio, ctrl + f5 run, find the page can not load images, js, json file.
Press F12 to view the error and found 500 errors. Js file open error, suggesting that:

IIS错误：在唯一密钥属性“fileExtension”设置为“.mp4”时，无法添加类型为“mimeMap”的重复集合项

Reference park blog solution: add in the web.config file:

<staticContent>
     <remove fileExtension=".json" />
     <mimeMap fileExtension=".json" mimeType="application/json" />
</staticContent>

problem solved.