compiling with 1.6.3 breaks with the error as in the title, but the same code compiles in 1.6.2, I think it has something to do with 'own' in for loops. but not sure yet.
I reproduce it but my code base is too big (and a proprietary project) so I need to work on narrowing it down
But i found someone who managed to reproduce it that also included the code:
https://groups.google.com/forum/#!topic/coffeescript/qiUWkPBJ3gM
I will update this issue soon once I get a small enough piece of code to reproduce as well.
EDIT: of course I didn't even bother to check and see that the sample in the link is a js file (which explains the "And what's your coffee ?" comment by @Nami-Doc ) sorry about that! :)