The H series errors are related to hosting configuration issues. The QuickBooks error H505 appears when one or more PCs are set as QuickBooks servers. If you're trying to use your computer in multi-user mode, then you ought to know that only the server can work like that. Therefore, your PC hosting the corporate files should be the sole PC configured because the host. If not, you'll find yourself with errors like H505.
 QuickBooks Error H505