This is a known issue at Google’s end and it likely happens when a Google user is logged into multiple Google accounts in the same Google Sheet.
If your default Google account is not the one that is associated with the Google add-on, the sidebar of the Google add-on may display a grey screen with the message “drive.google.com refused to connect”
Please open your Google Chrome in incognito mode and open the same Google Sheet while you are logged into a single Google account. The error should not appear.
Alternatively, you may visit http://accounts.google.com/logout and log out of multiple Google accounts. The error is displayed due to permission conflict between Google user accounts inside Google Sheets and Google Forms.
If you are still facing any issue with Google Drive refusing to connect, please post in the help forums.