Maybe your Incredimail file didn't download correctly or the download process was intrerrupted by something and the file is not complete.
Your file could be corrupt.In that case you should try to download it from another source.
If your Incredimail file that you downloaded contain viruses or spyware and you have installed an antivirus on your computer,the file will be blocked and you can't open Incredimail.You should delete the file if you can't clean the virus and download it from another site.

You can download Incredimail from here.
We downloaded it and can be opened.It works fine.