[Huxley]

This isn't my problem but my friend's, I checked his problem via Team Viewer.
When I opened the installer and clicked Run, an error window popped. It said: 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

That's all, I have no problem and the installation went smooth for me.

[Jay_]

The downloaded file is probably corrupt. Tell him to redownload it and try again.

Also, if you actually open that link, you will see a section called "How do I fix the problem?"

[newbienoob]

I faced this problem once. Just redownload again.

[Huxley]

Okay, he said he solved it. Thanks guys for your help.