Wish I could offer some direct help, but don't have a mac available to test ATM.
Are you seeing this problem directly after export, or after DL'ing your zip from dropbox to mac, then running? Cause I noticed this in Aurel's howto:
★ A note about Dropbox and Mac builds
Exported Mac builds works alright until you use Dropbox or this kind or services. The file properties can vanish (very often).
Compress your game in an archive before transfer (if possible, not only as a ZIP, as Dropbox handles it as a regular folder now. Changing the extension like a fancy .ZOP will assure Dropbox don't mess with your game)
Maybe 7z would be immune?
Also, if you go to "C:\Program Files\NodeWebkitForC2", what size are your osx32 and osx64 folders?
Considering your situation, you might try hitting up Ashley; maybe he would have some further ideas:
https://twitter.com/AshleyGullen