Full Error Message: 
“Error while creating new document. Error message: Error getting access token. Error: invalid_grant. Error description: Token has been expired or revoked”
1. You may be getting this error message when trying to generate a document and your Salesforce custom domain name has changed or you have a new server instance (example NA18).
2. Go to RS Documents Configuration tab and click “grant access” to reauthorize app and google drive.
3. From there see if you receive an error message referring to “Error: redirect_uri_mismatch”If you receive an error message when authorizing your Google Drive which refers to “URI misdirect” with custom domain, please go to AppExchange to upgrade your app package version to latest available. After you upgrade your package version, then proceed back to RS Documents Configuration tab to authorize app with your chosen google drive account.