Hi...I just paid for and received the email for my download of Grimrock 2.2.1.18 I downloaded it and extracted only to encounter this message for Installer integrity.

I've also redownloaded and tried again to no avail. How should I proceed to correct this? Thanks.
can't seem to get the image to post...so here's the link:
https://www.dropbox.com/s/pcifmjzrdbzxihk/nsis.jpg?dl=0