Error：Access to the dex task is now impossible、starting with 1.4.0

Error:Access to the dex task is now impossible, starting with 1.4.01.4.0 introduces a new Transform API allowing manipulation of the .class files.See more information: http://tools.android.com/tech-docs/new-build-system/transform-api

set your gradle version explicitly to 1.3.0 in dependencies section of build.gradle file
classpath 'com.android.tools.build:gradle:1.3.0'