One of my mates runs a Minecraft server for people from a certain forum. Now, I wanted to be able to fly and fast-mode and no-clip and stuff, so I downloaded the client. It all unpacked fine, I put the .jar in the lib and stuff, so that's all good.

Now, I ran the client, entered my password and username, and pasted the URL to my friend's server ni the box, and pressed Go!. I connected to a generated but apart from me empty map (though there were trees and sh*t) and I could fly there. Then my friend told me to close it and connect to his, but once I did that I could not use my powers on his server.

What could be wrong?