QuickBooks Error 1603 typically occurs when there is an issue during the installation or update of QuickBooks software. This error is generally caused by a corrupt download of the software, incomplete installation, or corruption in the Windows registry from a recent QuickBooks-related software change. Symptoms include the crashing of the active program window, Windows running sluggishly, and the computer freezing for a few seconds at a time. Resolving this error may require repairing the registry, performing a full malware scan of your computer, or updating the PC device drivers.