QuickBooks error msi returned 1603 can occur when trying to install or update QuickBooks on your computer, and it usually indicates a problem with the Microsoft Windows Installer. To fix the error, you can try several troubleshooting steps like running the QuickBooks Install Diagnostic Tool, updating your Windows operating system, or uninstalling and reinstalling QuickBooks. If the problem persists, you may need to contact QuickBooks support for further assistance at +1-855-948-3646.