The QuickBooks error H505 occurs due to an issue with multi-user hosting set up and when users try to access the company file on another PC. A damaged .ND file, incorrect hosting configurations settings are the main culprit for QuickBooks error code H505. First, you will have to make a new company file folder and replace the previous file to eliminate the problem. Another solution is to reconfigure the firewall settings and for that, go to the firewall settings, choose the advance setting option, right-click on outbound rules, and click new rule. Now you will have to click on ports and select next. Once you choose the right port, then click allow the connection and open QuickBooks in multi-user mode. These steps will resolve the QuickBooks error H505.