When installing. Net framework 4.0, you will encounter the following error page,

Next, I will post solutions for you

1. After inputting CMD in the start menu, the CMD command input window will pop up

2. Enter net stop wuauserv in the above CMD command line

3. Continue to enter echo% windir%

4. Change the name of the software distribution folder in the pop-up folder (usually C: Windows)

5. Continue to enter net start wuauserv  

6. Install net4.0 again and it will be successful

//If you think the above command is troublesome, you can paste and copy it to the CMD window with the mouse