It appears that some files of the new 0.8.3 release on sourceforge.net are corrupt. Not sure yet as to which files are really affected, but for now the alternative is to download zenmagick-0.8.3.zip from the zen-cart contribution section.

EDIT: I updated there core release file and tha apidocs but it might take a while before those changes are replicated onto the mirrors. Until then, please download from the zen-cart contribution.