This could happen for 1 of 3 reasons:
- A slow network connection.
- Some security software, or perhaps the computer is managed by a company (i.e. your employer) which prevents you from installing extensions.
- It might be a malware or a virus on your computer (unrelated to Stands, sorry) that prevents you from installing extensions.
If you think it's not the network connection, and your anti-virus is fine (or you don't have one), it could quite possibly be option number 3.
In that case, you might want to try and delete Chrome and re-install it. You can also try running the Google Malware Cleanup tool, found here: https://www.google.com/chrome/cleanup-tool/