When you extracted it, was there a 'gradients' folder present in the same location as the exe file?
The error is caused if that folder does not exist
Oh I see what the problem is now, I accidentally included the files twice in the zip file.. :)
You've probably got a folder structure like this:
If you go into the Windows folder, you'll see blastfx.exe again, run that version and it should work okay. I'll get the zip files fixed later