why block editor command is not working in my autocad2015? If we select the object, then enter command, its not working..All the times, I have to enter the command first and select the object second. Why this happens? 

Please try double click in the block- it will work

You could also try turning the multi functional grip menu off (it can sometimes interfere), or just stick with the classic click on the block, BE, double tap space bar, or just add it to the right click menu...