Minecraft Ps3 Can't mine Blocks?

I was playing minecraft searching for diamonds when I found a cave and some minutes later I found diamond however I can't mine it I have A diamond pickaxe with fortune 3 on it and I can't mine the diamonds or anything around it but when I get like 2-4 blocks away I can mine blocks again.

Sorry dude PS3/360 worlds have limits on worlds. The reason why you can't mind is because your on the edge of your world. Check your map to see where you are. If your on the edge when you get to your diamonds then you can't mine it

He's right you can't mine outside the boarder of your world, however if you are not at the edge of your world then it could very well be some minor lag, which if that is the case try saving your world and resetting your ps3