Started multi-player survival server with a few friends(3 total people including me) and wanted to give 1 map to each player like in Minecraft Xbox edition (This problem is for PC v1.4.2) so i changed my game-mode (while opped; I don't know if this problem happens when changed through console) and handed 1 map to each player (tested map, didn't cause problem; no items did) and changed my game-mode back to survival and found myself unable to mine / destroy any blocks. I could right click usable items such as furnace, door and chest just fine though. In order for me to fix this I had to delete my player file information from the server world folder.