attachment_fu + mini_magick troubleshooting

I've got a model with :has_attachment with content of image type.

When I'm trying to save an image, the following line in the log
appears:
Exception working with image: ImageMagick command (identify "C:/
WINDOWS/TEMP/minimagick2860-0") failed: Error Given

Minimagick is installed properly or seems to be. At least, all mini-
magick tests except those with some php-file are working.

What's that?
Thanks.