QuickBooks Error H303 typically appears when trying to access a company file located on another computer, and the connection to that server is disrupted or not properly configured. This error signifies issues with the network setup, preventing QuickBooks from reaching the server. Resolving it involves checking the hosting configuration, firewall settings, and ensuring the network setup supports multi-user access. QuickBooks users are advised to use the QuickBooks File Doctor Tool to diagnose and resolve network issues that might be causing this error.