Update QuickBooks to the latest release, create a new user account, and ensure that the QBDataServiceUser(XX) has appropriate permissions to access the file.

Steps to resolve error 6189 by setting appropriate access permissions for the folder that contains your company data file.

Troubleshoot and fix the problem where you can't open a multiuser company file but others are able to open it normally.

This article contains detailed instructions on how to download and install the QuickBooks Online Backup program.