app:clean classes Exception

Error:Execution failed for task ‘:app:clean‘.
> Unable to delete directory: C:\Users\LiuZhen\Desktop\umer_doc\app\build\intermediates\classes

解决方案：

allprojects {
    repositories {
        jcenter()
    }
    task clean(type: Delete) {
        delete rootProject.buildDir
    }
}

app:clean classes Exception

原文：http://www.cnblogs.com/LiuZhen/p/5455080.html