When QuickBooks multi-user mode not working correctly, it can hinder collaboration and data access within the software. This issue typically arises due to several common reasons. Firstly, ensure that all computers involved have stable network connections and are correctly set up to communicate with each other. Verify that QuickBooks is installed correctly on each workstation and that the QuickBooks Database Server Manager is running on the server computer. Check for any firewall or security software settings that might be blocking QuickBooks communication. Additionally, ensuring all users have the appropriate permissions to access and modify company files is essential. If problems persist, using QuickBooks File Doctor to diagnose and repair network-related issues or contacting QuickBooks support for more advanced troubleshooting may be necessary to restore multi-user functionality effectively.