Error: Runtime failure for task ': app: processDebugResources'. & gt; Unable to delete folder & ldquo; & rdquo; in Android studio


I am trying to develop a android application using android studio ,so i create an android app and i want to publish it ,when i clicked on build project ,i get this error :(i need the apk file)

Error:Execution failed for task ':app:processDebugResources'.
> Could not delete folder C:\Users\ehsan\AndroidStudioProjects\MyApplication3\app\build\generated\source\r\debug\com\example\ehsan

I am so new in android studio

Build.gradle :

apply plugin: ''

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.2"

    defaultConfig {
        applicationId "com.example.ehsan.myapplication"
        minSdkVersion 15
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), ''

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile ''

I guess some of the files in the target build directory is open in another tool you use. Just a file handle open in the folder which has to be cleaned. The build task 'clean' wants to delete all the files in the build directory(normally 'target') and when it fails, the build fails.