I remember I got that error a few times and that was not due to someone else claiming the faucet.
I had my freebitco account open in two different devices. I claimed the faucet on one of them without refreshing the page on the other one and therefore the "roll" button was still available on the other device. Since I could see the 'roll' button, after some minutes, I mistakenly thought that an hour has passed. I clicked on "roll" button and I got an error saying "Someone has already played from this IP in the last hour.".