flying is not enabled on this server what to do? (Minecraft)

Hi. Playing with your mine launcher. Yesterday jumped from Spawner to the lower world and in contact with it throws me from the server and writes the message flying is not enabled on this server. Cheats not ISP-th, and your launcher is written, they say we are protected from them. You can't come in, though managed to gain login with pass. and enter /home. Does not help. What could it be???