QuickBooks Error Code H505is related to issues with the multi-user hosting setup, preventing the computer from accessing the company file on another computer. 

• Ensure only the server or host computer has multi-user mode enabled. Go to the "File" tab section and then click on it. From there, you need to go to the "Utilities" and then head to the "Host Multi-User Access" tab.

• Install and then just run the QuickBooks Database Server Manager, and you have to do this on the server computer hosting the company file.

• Make sure the server computer is in the correct hosting mode. In the system tray, right-click the QuickBooks Database Server Manager icon and choose "Database Server Manager."

• Configure firewall settings to allow incoming/outgoing communication for QuickBooks. Add exceptions for QuickBooks programs.

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