I know nothing about miniMagick but it would help if you posted your code.
I assume you do have ImageMagick installed to use mininMagick ? If so you could try a couple of things using the comand line ( or php ) to prove your ImageMagick installation is OK first.
I have some code on my site to test for the correct paths etc. as that could be your problem.
http://www.rubblewebs.co.uk/imagemagick ... ommand.php