How come players can't break any blocks because it always reappears 2 seconds later. This isn't from lag since my internet is ok and It happens to me too. If they are OPs it's ok, how do I fix this?
Also if using a plugin such as worldguard/edit they have a spawn protection which could be the problem. Also do what @LightKing said look into permissions.
Spawn protection or it's a bugged chunk, seems to be happening more and more with these latest Bukkit builds. Not to mention the server is eating up resources like the Earth is eating up Japan.