QuickBooks errors 1603, 1601, and 1642 occur during the installation or update process. Error 1603 is a common installation error, often due to issues with the Microsoft .NET Framework or insufficient permissions. Error 1601 indicates a problem with the Windows Installer, potentially from an outdated or corrupt installer. Error 1642 usually involves issues with Windows updates or installer services. Resolving these errors typically involves repairing the .NET Framework, ensuring the Windows Installer is updated, and verifying system permissions.