QuickBooks in multi-user mode not working may encounter issues due to network configuration problems or database corruption. Common causes include firewall settings blocking access, outdated software versions, or insufficient user permissions. To resolve, start by updating QuickBooks to the latest version and ensuring all computers have stable network connections. Verify firewall settings to allow QuickBooks access through ports 8019, 56726, and 55358-55362. Repair QuickBooks installation via the Control Panel, and if issues persist, consider restoring a recent backup or contacting QuickBooks support for advanced troubleshooting. Regular updates and proactive network maintenance help prevent future disruptions in multi-user mode.
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