Upgrading from classic to hd
MultiBit developer here. You should be able to simply spend from your Classic wallet into your new HD wallet. Don't try moving private keys around - that's really easy to get wrong and is one of the reasons we wrote HD in the first place.

There are full instructions on upgrading on the MultiBit website: https://multibit.org/en/help/hd0.1/how-to-upgrade-from-classic.html