错误：在将项目从Eclipse导入到Android Studio之后，任务'：app：dexDebug'的执行失败

我将一个项目从Eclipse导入到Android。然后我尝试运行应用程序时收到此错误消息：

I imported a project from Eclipse to Android. Then I get this error message after I tried to run application:

错误：执行失败的任务'：app：dexDebug'。
com.android.ide.common.process.ProcessException：org.gradle.process.internal.ExecException：Process'command'C：\Program Files（x86）\Java\jdk1.8.0_40\ bin \java.exe完成了非零退出值2

Error:Execution failed for task ':app:dexDebug'. com.android.ide.common.process.ProcessException: org.gradle.process.internal.ExecException: Process 'command 'C:\Program Files (x86)\Java\jdk1.8.0_40\bin\java.exe'' finished with non-zero exit value 2

看起来像这样的问题：
错误：任务'：app：dexDebug'的执行失败。 com.android.ide.common.process.ProcessException

It seems like this problem: Error:Execution failed for task ':app:dexDebug'. com.android.ide.common.process.ProcessException

但我试过所有的答案，没有一个工作。

But I tried all of the answers and none of them worked.

这是我的build.gradle

Here is my build.gradle

apply plugin: 'com.android.application'

android {
  compileSdkVersion 21
  buildToolsVersion "22.0.1"
  compileOptions.encoding = 'windows-1251'

  defaultConfig {
    applicationId "sk.app"
    minSdkVersion 15
    targetSdkVersion 21
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_7
        targetCompatibility JavaVersion.VERSION_1_7
    }
  }

  buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
    }
  }
}

dependencies {
  compile 'com.android.support:support-v4:23.1.1'
  compile 'com.google.code.gson:gson:2.3'
  compile files('libs/activation.jar')
  compile files('libs/droidText.0.4.jar')
  compile files('libs/google-play-services.jar')
  compile files('libs/mail.jar')
}