Local value 72mb means you have not edited the file correctly or your server does not support ini_set overrides
You would need to have your host give you the path to mogrify and enter that in your config settings then switch global options to imagemagick and try.
So after clearing your uploads directory are you able to say upload a small image as a test. There are alot of info here you can not process a 4mb image with GD2 that will crash PHP every single time so it that is how your testing you might want to try a different image.
I really can not give any more hints without seeing the actual site here.