Hey, @jamesbrown,
The reason that the SMART wallets on Cryptopia and HitBTC are down is because the devs released a new code and new wallets in prep for the SmartNode release (similar to Dash's Master Nodes), so the exchanges are currently updating their backends to have the correct codes in place for use of the new wallets. They should both be back online in the next couple of days or even sooner - Depends on that particular exchange's devs.
Cryptopia halted their exchange and wallet, HitBTC only halted their wallets, so people that had their SMART on HitBTC are still able to trade, they just can't deposit/withdraw yet.

Hope that answers your question!

_{Edit: Self upvoted for visibility to your viewers. :)}