QuickBooks Error H505 occurs when trying to switch to multi-user mode, typically due to improper hosting configurations or communication issues with the server. This error indicates that the QuickBooks software cannot access the company file on another computer. Common causes include incorrect DNS settings, firewall blockage, or QuickBooks services not running. Dial 1.855.738.2784 for expert assistance in resolving QuickBooks Error H505 and restoring seamless multi-user access to your company file.