@eeeooo:
What browser are you using? Have you tried the Mega app (either mobile or PC)?
The thing I'm thinking, as I've bumped into before, is that some browsers have a memory cap... downloads larger than that will fail leaving a broken archive if "downloaded", or will result in an error message.
Try downloading the Mega application, and try to sync using that.
FWIW, I've otherwise NEVER had an issue with Mega. It's a great service; it's as good, if not better than Dropbox! Good luck, post your results.