Why do I get NSIS Error?

A NSIS Error message box means the installer you're trying to run is corrupted. It means the installer data was somehow modified and is no longer valid. The error states:

Installer integrity check has failed. Common causes include
incomplete download and damaged media. Contact the
installer's author to obtain a new copy.

More information at:
http://nsis.sf.net/NSIS_Error

In versions prior to 2.35, the error states:

The installer you are trying to use is corrupted or incomplete.
This could be the result of a damaged disk, a failed download or a virus.

You may want to contact the author of this installer to obtain a new copy.

It may be possible to skip this check using the /NCRC command line switch
(NOT RECOMMENDED).

Solutions

Follow these steps for each case to get rid of the error.

Error with Single Installer

1. Clear your browser's cache.
2. Disable any download accelerators and download the installer again.
3. Update any active anti-virus and download the installer again.
4. Disable any active anti-virus and download the installer again.
5. Download the installer from another source. It might be corrupted on the server, or the connection to the server is unreliable.
6. Download the installer using another computer and copy it to the original computer using a reliable medium.
7. Rename the installer so it is a simple one-word name with no special characters (without removing the .exe suffix)

As a last resort, the installer can be executed even though it's corrupted. To bypass the corruption test, pass /NCRC on the command line. To do so, go to Start->Run, type cmd and hit Enter. A black console window should open. Drag the installer into the window, hit Space and type /NCRC. Hit Enter again and the installer should start. This is not recommended!

Error with Multiple Installers

1. Clear your browser's cache.
2. Disable any download accelerators and download the installer again.
3. Disable any firewalls and download the installer again.
4. If it is installed, uninstall the nVidia firewall and download the installer again.
5. Scan for, and remove malware
6. Scan for, and remove viruses
7. Scan the hard drive using scandisk, chkdsk, or any other hard drive repair tool
8. Download the installer using another network connection and copy it to the original computer using a reliable medium.

Random or Start-up Errors

1. Scan for, and remove malware

Error When Closing Internet Explorer

1. Try updating McAfee manually. Failed updates of McAfee have been known to produce this problem.
2. Scan for, and remove malware