Error 1603 while installing/uninstalling?

Error 1603: Fatal Error During Installation
Problem
When running an installation, you receive the following error message:

"Error 1603: Fatal Error During Installation"
Or you may get the following error:

"Error 1603: General Windows Installer engine error. Increase DiskSpace requirement in Setup.ini and try again."
Fix
Error 1603 is a generic machine-specific issue. One or more of the following fixes may resolve the error.

This error is known to occur on computers that do not have enough disk space for the installation. To increase your hard disk space, follow the instructions in How Do I Increase Hard Disk Space on My Computer?
The Temp directory is not clean. To clean the Temp directory, follow the instructions in Clean the Temp Directory.
A certain file on the machine is locked. To fix this:
Close all applications running in the background.
Reboot your computer.
Run the installation again.
If you are using Windows 95, 98, ME, 2000, or NT, the Windows Installer Service may not be properly installed on the machine. Update the system with the latest Windows Installer Service by following the instructions in How Do I Install the Windows Installer Engine on My Computer?
On Windows NT, 2000, or XP, make sure you have administrative privileges. To confirm you have administrative privileges, follow the instructions in Acquire Administrative Privileges on Your Computer.
Use Microsoft’s Windows Installer Cleanup utility to remove traces of previous installations. This utility does not remove files installed by the installation, which may need to be removed manually. For more information, refer to Microsoft’s Knowledge Base article Description of the Windows Installer CleanUp Utility.
Additional Information
Another reason your installation may not run is changes to your computer caused by recent updates. For example, updates to your operating system may cause installations created prior to the update to fail. You may want to uninstall any recent updates, install your application, and reinstall the update. WARNING: You should check with the software vendor who created the update to ensure no adverse affects will result from uninstalling the update.

Glossary Terms
administrative privileges, Temp directory

Does Your Issue Still Exist?
If after following these instructions your product failed to install, you'll need to contact your vendor. See the Who to Contact page for more information.