If you've created the wallet before the HD function was introduced with SmartCash, then you definitely won't be able to use the HD feature right off the bat. Existing wallet can't be converted to HD wallets and you will have to create a new wallet to use it.
Steps to create a new HD wallet.
1) Go to %appdata%/SmartCash.
2) Rename wallet.dat to wallet-old.dat
3) Open SmartCash Node Client Wallet.
4) Wait for it to load and go to the addresses tab to get an address. Also make a backup. Then shut it down.
5) Rename the new wallet.dat to wallet-HD.dat.
6) Rename wallet-old.dat to wallet.dat
7) Start up SmartCash Node Client Wallet and send the coins to the address generated with your HD wallet.
8) Shut it down.
9) Move the old wallet.dat from the folder and rename wallet-hd.dat back to wallet.dat and you would be able to use the HD wallet.