为什么unity编译时gradle报错

CommandInvokationFailure: Gradle build failed.
/Library/Java/JavaVirtualMachines/jdk1.8.0_144.jdk/Contents/Home/bin/java -classpath "/Applications/Unity/PlaybackEngines/AndroidPlayer/Tools/gradle/lib/gradle-launcher-4.0.1.jar" org.gradle.launcher.GradleMain "-Dorg.gradle.jvmargs=-Xmx2048m" "assembleRelease"
stderr[

FAILURE: Build failed with an exception.

* What went wrong:
A problem occurred configuring root project 'gradleOut'.
> Cannot add task ':prepareUnityAdsLibrary' as a task with that name already exists.

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

BUILD FAILED in 1s
]
stdout[
NDK is missing a "platforms" directory.
If you are using NDK, verify the ndk.dir is set to a valid NDK directory. It is currently set to /Users/JasonXu/Downloads/android-sdk-macosx/ndk-bundle.
If you are not using NDK, unset the NDK variable from ANDROID_NDK_HOME or local.properties to remove this warning.

]
exit code: 1
UnityEditor.Android.Command.WaitForProgramToRun (UnityEditor.Utils.Program p, UnityEditor.Android.WaitingForProcessToExit waitingForProcessToExit, System.String errorMsg)
UnityEditor.Android.Command.Run (System.Diagnostics.ProcessStartInfo psi, UnityEditor.Android.WaitingForProcessToExit waitingForProcessToExit, System.String errorMsg)
UnityEditor.Android.AndroidJavaTools.RunJava (System.String args, System.String workingdir, System.Action`1 progress, System.String error)
UnityEditor.Android.GradleWrapper.Run (System.String workingdir, System.String task, System.Action`1 progress)
Rethrow as GradleInvokationException: Gradle build failed
UnityEditor.Android.GradleWrapper.Run (System.String workingdir, System.String task, System.Action`1 progress)
UnityEditor.Android.PostProcessor.Tasks.BuildGradleProject.Execute (UnityEditor.Android.PostProcessor.PostProcessorContext context)
UnityEditor.Android.PostProcessor.PostProcessRunner.RunAllTasks (UnityEditor.Android.PostProcessor.PostProcessorContext context)
UnityEngine.GUIUtility:ProcessEvent(Int32, InPtr)
这是什么原因？
麻烦大佬解释
还有以下这个错误
UnityEditor.BuildPlayerWindow+BuildMethodException: 3 errors
at UnityEditor.BuildPlayerWindow+DefaultBuildMethods.BuildPlayer (BuildPlayerOptions options) [0x0020e] in /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPlayerWindowBuildMethods.cs:181
at UnityEditor.BuildPlayerWindow.CallBuildMethods (Boolean askForBuildLocation, BuildOptions defaultBuildOptions) [0x00065] in /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPlayerWindowBuildMethods.cs:88
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)
这些是什么情况？？