On a multi-user network, QuickBooks Error H303 happens when the program is unable to access the corporate file. This typically occurs as a result of improper network configuration, firewall limitations, or hosting problems.  In order to restore seamless QuickBooks operation, fixing it entails confirming network connectivity, modifying firewall settings, and making sure the hosting configuration is correct. A QuickBooks consultant can be reached at 1.855.738.2784.