The private keys you want to import cannot be the encrypted_privkey output. You must use dumpwallet with the passphrase to get the unencrypted private keys. Those keys should start with '5', 'K', or 'L'. If they don't, then something is wrong.

You could use Electrum. It is a very good wallet and you can import your private keys there, although I recommend that you actually create a wallet with Electrum and then sweep your exported private keys. That way you can have your Bitcoin in the safety of a HD wallet.