An admin will check this out, we spoke about this in-game, but no admin was online at that moment. Thanks for posting about this on the forums, makes the process go by much smoother.
This same issue was posted about by another member last week, The problem is caused by glitching inside of a block and our hack prevention mistakes your irregular avatar movement as flying. If you are using a client, turn it off. (Do not use it again on this server.) This may fix your problem. If you are not using a client, try getting a friend to skype you and have them go on the server and find where you are trapped, then brake the block you are trapped in. The best way to do this would be to join the server and instantly press F3, opening your cords in the top left of the screen. Get you X, Y & Z then tell your friend the cords, Once the block you are in is broken, you will be free to join the server again. Hope this helped your problem. If you have any questions, feel free to ask.