The QuickBooks Error H505 occurs when there is more than one of your workstations set as the server of your QuickBooks software. To resolve this issue, you just need to disable the HOst Multi-User Access from all other computers except the one that hosts your company files, the main computer. If doing this doesn’t solve your problem, then you can contact QuickBooks Technical Support for assistance and let them diagnose the root cause of your issue and work on the fix. You can give us a call on our helpline or chat with our agents online to get support anytime.