Yes, there are limits on your room cards. If you reach your limit, you may call your resort front desk, have them apply the amount onto your CC, or whatever you put down for the room charge, and start all over. That still doesn't help if the system is down, or they just don't accept the room charges.
That being said, if you are staying at a value, you get a $500 limit, moderates get a $1000 limit and deluxes get $1500. I have no idea how they determined these limits, and have never found anyone who could explain it.