Dragonfly::ImageMagickUtils::ShellCommandFailed in ...

I'm really new to refinery and fairly new to rails overall. I've
succesfully installed refinery and it's working great, except when I
want to add an image. I get the following error:
Dragonfly::ImageMagickUtils::ShellCommandFailed in Admin/
imagesController#create
I'm not sure what might be causing this but I've created a few
different projects and I keep getting the error. I've noticed that in
the settings, it calls for a "Dragonfly Secret" but it's already
populated. Could this be wrong?
Thanks for any help you can provide,
---------------------------
Is it possible that you don't have ImageMagick installed?
https://github.com/resolve/refinerycms#readme <-- link under "Requirements"