Well you would need to pass that error to your host. There is very little anyone could assist with on a windows server as you need backend access which of course only your host has. That looks like an issue with the php exec function. I do not find anything on the internet about that specific error.
1. They would install Imagemagick in a short directory like so
2. Make sure your data and uploads directory as well as cmd.exe has READ WRITE EXECUTE permissions.
3. You can then try uploading. If you get permissions errors one last thing to try
4. You edit image-inc.php and change this line to NT
Content visible to verified customers only.
If all that fails then you might need to use GD2 because sometimes getting Imagemagick to work can be difficult. It is all permissions related.