When you try to install a Google Chrome extension show the following error message:
An error has occurred
Download was not a CRX
RELOAD CLOSE
Effect:
Not install the required extension.
Solution from your comments: (Prefered because it respects your privacy but not always works)
Open Google Chrome,
click the Chrome menu 
on the browser toolbar then select New incognito window
or
press Ctrl+Shift+N
then open the page of extension in this mode, if you don’t know the url you can copy and paste in the incognito window the following:
https://chrome.google.com/webstore/category/extensions
search the extension and click on ADD TO CHROME to install.
Note: If you chose this solution you have to repeat the above steps everytime you want to install a new extension because it will always appear the same error. Whenever, you have to open an incognito window.
My Solution:
Sign in into Google before to try to install an extension.
To Sign in or Sign up in to Google Chrome, open Google Chrome
click the Chrome menu on the browser toolbar then select Sign in to Chrome
or
using the following link:
Google Accounts
Did my solution solve your problem? Leave a reply.