If you receive this error message it generally means there has been a failure in renewing the access token - the security credentials for the session.
Log out of your XC account.
Go to drive.google.com and sign out.
Sign in to XC and attempt to access your google drive
If this fails then...
Close open browsers.
Open a fresh browser.
Login to drive.google.com.
Click on the cog on the top right and select Settings.
Select Manage apps.
Disconnect cloud.xara from the drive.
Log back into your account.
At this stage you might see this screenshot...
Click on Allow then try and access the cloud drive.