Hi,
I recently had this problem too. Seems that the newer version of PHP has made some changes to the image create function.
What you need to do is open zen/i.php
--Go to Line 88-
Before line:
imagejpeg($newim, $newfile, $image_quality);
--Add line--
$fp=fopen($newfile,"w");fclose($fp);
Save and re-upload. This should work!