You always need to have some ethereum balances to send out any ethereum based tokens from your wallet. Gas is nothing but tx fees like what we have in bitcoin transactions. In ethereum environment you need to pay tx fees in ethereum regardless of you will be transacting any ethereum based tokens.

Have some ethereum balances in your wallet well before trying to resend your tokens next time.

You may like to read more on this here : https://www.myetherwallet.com/#help