What operating system are you using? and are you using the itch.io version, or the Steam version?
Viewing post in Error: Unable to open gradient preset directory!
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:
BlastFX.exe
BlastFX.pck
Windows
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