I just bought minecraft today (Last day of alpha) and me and my friend decided to venture into the multiplayer aspect of the game. Since his computer is about twice as fast as mine (4gb of ram, An i5 processor? No idea what that is, not a computer whiz) he ideally would host the server.
He was able to start a server and I was able to join it, however that is when problems arose. We kept running into this problem where my character would suddenly stop having the ability to build blocks and would take damage out of nowhere. We eventually realized that in my friends game I had been in one spot the entire time but in my game I was running around having a merry time.
Not only that but we can only break some blocks, others regenerate, and yes we both are OP's. So if someone is able to help me and my buddy with this I would greatly appreciate it.