+1
No MD5 match on either the direct download link at Zentyal (twice) nor the sourceforge link provided by ChrisG). Only been trying the 64 bit (zentyal-3.3-amd64.iso). Will continue trying the various mirrors (though mirrors, by definition, SHOULD have exactly the same file and MD5 sum).
I wouldn't consider this actually "solved" if one out of many downloads actually works.
Edit--
Got it by copying download link and using wget instead of clicking in a browser. I did make a couple other changes trying other things so can't be sure this is what did the trick (or maybe I finally just got lucky?
)