I didnt realise it was optional to pay a transaction fee, how would I override that if it ever happens again?
Well, with the Bitcoin-Qt client there is no override. If it says you must pay a fee it is because it looked at a few critieria and determined that miners will not accept your transaction unless a fee is paid. You options are to pay the fee or not make the transaction at that time.
What psy meant with that option 3 is that if you were to wait a day and make that exact same transaction you probably could do so without paying a fee. That's because one of the criteria the Bitcoin-Qt client considers is the age of the coins used in a transaction. If you just received a coin and then try to quickly spend the funds, that is similar to what a disruptive attack on bitcoin might look like, so by requiring a fee for those types of transactions makes it expensive for someone to try to abuse the bitcoin network by churning transactions over and over without paying a fee.
Other clients may not have such restrictions. Blockchain.info/wallet, for example, lets you choose "custom" mode where you get to choose the amount of a fee you pay. If you choose 0, it will let you. That doesn't mean your transaction will confirm in a timely manner, it just means that client isn't going to stop you from trying.
