How to rollback using cancel button of message box while using custom installer?

[prashant82]

I am using custom installer in my project . After welcome screen I have a custom form which has checkbox on it. After user selects checkbox then MessageBox dialogue pops up for YES|NO to proceed?
If response is YES , then I am copying some files.
If response is NO, I have to exit the entire set up, which is not happening currently. Files are getting copied too. On Cancel dialogue result

 Application.Exit(); or Environment.Exit(0);or Environment.Exit(1);

<br> is not helpful.
Please guide.

TIA
Prashant