Have you tried using it on MultiBit Classic?
https://multibit.org/release-info/classic/v0.5.19.htmlFairly sure the HD wallets are named something like "mbhd.wallet.aes". If it is just "multibit.wallet", it is most likely a MultiBit Classic wallet
NOTE: attempting to send coins out of MBC may result in transactions with very low fees by "modern" standards... You may be better off exporting you private keys and then importing or sweeping them into a more up to date (and maintained) wallet like Electrum.
Alao, I don't recommend MB HD, it has some serious bugs at the moment...