QuickBooks Error H303 multi-user Hosting occurs when a user attempts to switch QuickBooks to multi-user mode and the server hosting the company file cannot be accessed. This error indicates that additional configuration is required to ensure that the workstation can communicate with the server. Common causes include incorrect network setup, firewall settings blocking communication, or a misconfigured QuickBooks database server manager. Resolving Error H303 typically involves adjusting firewall settings and verifying network connectivity. For help with ongoing problems, call 1.855.409.2300 to speak with a licensed professional or QuickBooks support.