When QuickBooks multi-user mode not working, it prevents multiple users from accessing the company file simultaneously, disrupting workflow. This issue may arise due to incorrect hosting settings, firewall configurations, or damaged network data files. To resolve this, ensure the server computer is hosting the file, adjust firewall and antivirus settings, or use QuickBooks File Doctor to fix network issues. For expert assistance, dial 1.855.738.2784 and get your QuickBooks back on track.