Installer integrity check has failed error

I recently downloaded NSIS on my Windows Vista machine. After this install I rebooted my machine and after a reboot I tried to install software application, and it throws up an error message.
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
The NSIS error keeps coming up anytime I try to install any software. Does this mean that I have a virus on my machine after I installed the software? Or does it mean that my installer is corrupt?
