Error 1603 is really dumb error.
You receive an "error 1603: A fatal error occurred during installation" error message when you try to install a Windows Installer package
Symptoms
When you try to install a Microsoft Windows Installer package, you may receive the following error message:
Error 1603: A fatal error occurred during installation.
If you click OK in the message box, the installation rolls back.
Cause
You may receive this error message if any one of the following conditions is true:
Windows Installer is attempting to install an app that is already installed on your PC.
The folder that you are trying to install the Windows Installer package to is encrypted.
The drive that contains the folder that you are trying to install the Windows Installer package to is accessed as a substitute drive.
The SYSTEM account does not have Full Control permissions on the folder that you are trying to install the Windows Installer package to.
You notice the error message because the Windows Installer service uses the SYSTEM account to install software.
I get this frequently with CRM plugin installer as well.
Most of the time is because of lingering remnants of previous installation.