Config Error Cannot add duplicate collection entry of type 'mimeMap' with unique key attribute 'fileExtension' set to '.docx' for UPK

this error receive when try to open http://localhost/KContent and educations after installition upk.

PROBLEM

HTTP Error 500.19 - Internal Server Error
The requested page cannot be accessed because the related configuration data for the page is invalid.
Module CustomErrorModule
Notification SendResponse
Handler StaticFile
Error Code 0x800700b7
Config Error Cannot add duplicate collection entry of type 'mimeMap' with unique key attribute 'fileExtension' set to '.docx'
Config File \\?\C:\KContent\web.config

Config Source

  163:       <mimeMap fileExtension=".ex~" mimeType="application/octet-stream" />
  164:       <mimeMap fileExtension=".docx" mimeType="application/vnd.openxmlformats-officedocument.wordprocessingml.document" />
  165:       <mimeMap fileExtension=".flv" mimeType="video/x-flv" />

SOLUTION

1.open the C:\KContent\web.config

2.add below lines between <staticContent>  tags.

 <remove fileExtension=".flv" />
 <remove fileExtension=".docx" />
 <remove fileExtension=".ex~" />

3.saved the web.config


ref:UPK: Importing a Title into Knowledge Center Fails with HTTP Error 500.19 Internal Server Error (Doc ID 1521720.1)