It means you are getting a lot of hits! You are alotted a certain amount of pages looked at per month and once you exceed that no one will be able to see your site for the rest of the month unless you increase your bandwidth.
That or you've been uploading a ton a slow loading images to your site.
I did the Diaper Hunt one year and all of our sites were down within a day because we had so many hits. Just email up your host and see how much it would cost to get more for this month and you might want a permanent increase if you are getting a lot of traffic.