QuickBooks Error 100 often appears when QuickBooks cannot communicate with the company file due to database errors. The issue may arise from restricted folder permissions, damaged server components, or incomplete QuickBooks installation. To fix it, restart the QuickBooks services, verify that your firewall isn’t blocking access, and run the Database Server Manager tool. If the problem persists, reinstalling QuickBooks may be required. Always ensure your system and server are configured correctly, as a stable environment reduces the chances of encountering QuickBooks Error 100.