If you are familiar with the signs and symptoms listed below, identifying QuickBooks error 1603 becomes simple. So, here are some of the causes of this error: 1. Microsoft NET 1.1 SP1 installation was uninstalled. 2. If the user is using an older version of QuickBooks 3. QuickBooks 1603 error can also be caused because of a problem while installing Microsoft.NET Framework 4. Installation is restricted due to a lack of ‘Permissions. 5. The QuickBooks files have become corrupted. 6. Because of a problem with the ‘Microsoft Windows Installer.'