I've followed the same steps using the new MyEtherWallet interface and I have encountered absolutely no error, even if while using the old interface I have had various issues.
I didn't even have to use the workaround published in another article by the team.
All in one, if I would have followed ALL the steps exactly as they were described above, I would have saved a few $ that I have now lost for unsuccessful transactions fees.

Thanks to the Sparkster team for the support!