If you hadn't made a deposit yet, where did your account balance come from? A lot of new players get confused over what constitutes bonus dollars. Anything they "give" you to start playing on at a site is basically bonus dollars. There are always strings attached. Most of the time you do have to invest some of your own money before you can withdraw any of theirs, or any of your winnings off of theirs.
I found this out the hard way at Noble Poker when I received a $10 "new player bonus" for opening an account, grew it to a bit over $300 playing ring games in three weeks, then tried to cash out $100 of it to deposit on another site. I was told that before I could make any withdrawals, I had to make a real money
deposit in the minimum amount of what I was withdrawing. In other words, to get $100 of what I won from their new player money, I had to deposit $100. Didn't make much sense, so I just blew it all on one big buy-in freeroll.