Unable to convert classes into dex format.

I'm working on a project using Unity 4.3 Pro and Vuforia 2.8. The project builds and works alright on iOS, but when I try to export an Android APK the built fails with the following error:

Error building Player: CommandInvokationFailure: Unable to convert classes into dex format. See the Console for details. java -Xmx1024M -Dcom.android.sdkmanager.toolsdir="/Applications/android-sdk-macosx/tools" -Dfile.encoding=UTF8 -jar "/Applications/Unity/Unity.app/Contents/BuildTargetTools/AndroidPlayer/sdktools.jar" -   stderr[   UNEXPECTED TOP-LEVEL EXCEPTION: java.lang.IllegalArgumentException: already added: Lcom/qualcomm/QCAR/BuildConfig; at com.android.dx.dex.file.ClassDefsSection.add(ClassDefsSection.java:122) at com.android.dx.dex.file.DexFile.add(DexFile.java:161) at com.android.dx.command.dexer.Main.processClass(Main.java:685) at com.android.dx.command.dexer.Main.processFileBytes(Main.java:634) at com.android.dx.command.dexer.Main.access$600(Main.java:78) at com.android.dx.command.dexer.Main$1.processFileBytes(Main.java:572) at com.android.dx.cf.direct.ClassPathOpener.processArchive(ClassPathOpener.java:284) at com.android.dx.cf.direct.ClassPathOpener.processOne(ClassPathOpener.java:166) at com.android.dx.cf.direct.ClassPathOpener.processDirectory(ClassPathOpener.java:229) at com.android.dx.cf.direct.ClassPathOpener.processOne(ClassPathOpener.java:158) at com.android.dx.cf.direct.ClassPathOpener.process(ClassPathOpener.java:144) at com.android.dx.command.dexer.Main.processOne(Main.java:596) at com.android.dx.command.dexer.Main.processAllFiles(Main.java:498) at com.android.dx.command.dexer.Main.runMonoDex(Main.java:264) at com.android.dx.command.dexer.Main.run(Main.java:230) at com.android.dx.command.dexer.Main.main(Main.java:199) at com.android.dx.command.Main.main(Main.java:103) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at SDKMain.main(SDKMain.java:129) 1 error; aborting ] stdout[ processing archive bin/classes.jar... processing com/unity3d/player/a$1.class... processing com/unity3d/player/a$2.class... processing com/unity3d/player/a$a.class... processing com/unity3d/player/a.class... processing com/unity3d/player/b$1.class... processing com/unity3d/player/b$2.class... processing com/unity3d/player/b.class... processing com/unity3d/player/c.class... processing com/unity3d/player/d$1.class... processing com/unity3d/player/d$2.class... processing com/unity3d/player/d.class... processing com/unity3d/player/e.class... processing com/unity3d/player/f.class... processing com/unity3d/player/g.class... processing com/unity3d/player/h.class... processing com/unity3d/player/i.class... processing com/unity3d/player/j$1.class... processing com/unity3d/player/j.class... processing com/unity3d/player/NativeLoader.class... processing com/unity3d/player/k.class... processing com/unity3d/player/ReflectionHelper$1.class... processing com/unity3d/player/ReflectionHelper$a.class... processing com/unity3d/player/ReflectionHelper.class... processing com/unity3d/player/l.class... processing com/unity3d/player/m$1.class... processing com/unity3d/player/m$2.class... processing com/unity3d/player/m$3.class... processing com/unity3d/player/m.class... processing com/unity3d/player/n.class... processing com/unity3d/player/o.class... processing com/unity3d/player/UnityPlayer$1.class... processing com/unity3d/player/UnityPlayer$2.class... processing com/unity3d/player/UnityPlayer$3.class... processing com/unity3d/player/UnityPlayer$4.class... processing com/unity3d/player/UnityPlayer$5.class... processing com/unity3d/player/UnityPlayer$6.class... processing com/unity3d/player/UnityPlayer$7.class... processing com/unity3d/player/UnityPlayer$8.class... processing com/unity3d/player/UnityPlayer$9.class... processing com/unity3d/player/UnityPlayer$10.class... processing com/unity3d/player/UnityPlayer$11.class... processing com/unity3d/player/UnityPlayer$12$1.class... processing com/unity3d/player/UnityPlayer$12.class... processing com/unity3d/player/UnityPlayer$13.class... processing com/unity3d/player/UnityPlayer$14.class... processing com/unity3d/player/UnityPlayer$15.class... processing com/unity3d/player/UnityPlayer$16.class... processing com/unity3d/player/UnityPlayer$17.class... processing com/unity3d/player/UnityPlayer$18.class... processing com/unity3d/player/UnityPlayer$19.class... processing com/unity3d/player/UnityPlayer$a.class... processing com/unity3d/player/UnityPlayer$b.class... processing com/unity3d/player/UnityPlayer.class... processing com/unity3d/player/UnityPlayerActivity.class... processing com/unity3d/player/UnityPlayerNativeActivity.class... processing com/unity3d/player/UnityPlayerProxyActivity.class... processing com/unity3d/player/p.class... processing com/unity3d/player/q$1.class... processing com/unity3d/player/q.class... processing com/unity3d/player/WWW.class... processing org/fmod/FMODAudioDevice$a.class... processing org/fmod/FMODAudioDevice.class... processing org/fmod/a.class... processing archive plugins/./QCAR.jar... processing com/qualcomm/QCAR/BuildConfig.class... processing com/qualcomm/QCAR/QCAR.class... processing com/qualcomm/ar/pl/BuildConfig.class... processing com/qualcomm/ar/pl/CameraPreview.class... processing com/qualcomm/ar/pl/DebugLog.class... processing com/qualcomm/ar/pl/ARHttpParams.class... processing com/qualcomm/ar/pl/SurfaceManager$1.class... processing com/qualcomm/ar/pl/RenderManager$1.class... processing com/qualcomm/ar/pl/SystemTools.class... processing com/qualcomm/ar/pl/ARHttpResponse.class... processing com/qualcomm/ar/pl/ARHttpRequest.class... processing com/qualcomm/ar/pl/CameraPreview$1.class... processing com/qualcomm/ar/pl/RenderManager$FixedFrameRateRunner.class... processing com/qualcomm/ar/pl/ARHttpClient$HttpResponseCallable.class... processing com/qualcomm/ar/pl/FileTools$AssetFileInfo.class... processing com/qualcomm/ar/pl/ImageTools.class... processing com/qualcomm/ar/pl/RenderManager$RenderRequestWatcher.class... processing com/qualcomm/ar/pl/ARHttpClient$HttpResponseWatcher.class... processing com/qualcomm/ar/pl/FileTools.class... processing com/qualcomm/ar/pl/SurfaceManager.class... processing com/qualcomm/ar/pl/SensorController.class... processing com/qualcomm/ar/pl/ARHttpClient.class... processing com/qualcomm/ar/pl/CameraPreview$CameraCacheInfo.class... processing com/qualcomm/ar/pl/RenderManager.class... processing com/qualcomm/ar/pl/SensorController$SensorCacheInfo.class... processing com/qualcomm/ar/pl/CameraSurface.class... processing archive plugins/./QCARUnityPlayer.jar... ignored resource META-INF/MANIFEST.MF processing com/qualcomm/QCARUnityPlayer/BuildConfig.class... processing com/qualcomm/QCARUnityPlayer/DebugLog.class... processing com/qualcomm/QCARUnityPlayer/OrientationUtility.class... processing com/qualcomm/QCARUnityPlayer/QCARPlayerNativeActivity$1.class... processing com/qualcomm/QCARUnityPlayer/QCARPlayerNativeActivity$UnityInitializer.class... processing com/qualcomm/QCARUnityPlayer/QCARPlayerNativeActivity.class... processing com/qualcomm/QCARUnityPlayer/QCARPlayerSharedActivity$1.class... processing com/qualcomm/QCARUnityPlayer/QCARPlayerSharedActivity$IUnityInitializer.class... processing com/qualcomm/QCARUnityPlayer/QCARPlayerSharedActivity$InitQCARTask.class... processing com/qualcomm/QCARUnityPlayer/QCARPlayerSharedActivity$InitUnityTask.class... processing com/qualcomm/QCARUnityPlayer/QCARPlayerSharedActivity.class... processing archive plugins/./Vuforia.jar... processing com/qualcomm/vuforia/CylinderTarget.class... processing com/qualcomm/vuforia/BuildConfig.class... processing com/qualcomm/vuforia/ImageTargetBuilder.class... processing com/qualcomm/vuforia/Vuforia$1.class... processing com/qualcomm/vuforia/Vuforia$UpdateCallbackInterface.class... processing com/qualcomm/vuforia/Type.class... processing com/qualcomm/vuforia/Vec3I.class... processing com/qualcomm/vuforia/CameraDevice$CAMERA.class... processing com/qualcomm/vuforia/Obb2D.class... processing com/qualcomm/vuforia/VideoBackgroundConfig.class... processing com/qualcomm/vuforia/TrackableSource.class... processing com/qualcomm/vuforia/RectangleInt.class... processing com/qualcomm/vuforia/VirtualButton.class... processing com/qualcomm/vuforia/Vuforia.class... processing com/qualcomm/vuforia/WordList.class... processing com/qualcomm/vuforia/VirtualButton$SENSITIVITY.class... processing com/qualcomm/vuforia/PIXEL_FORMAT.class... processing com/qualcomm/vuforia/MultiTargetResult.class... processing com/qualcomm/vuforia/Matrix44F.class... processing com/qualcomm/vuforia/TextTracker$UP_DIRECTION.class... processing com/qualcomm/vuforia/DataSet$STORAGE_TYPE.class... processing com/qualcomm/vuforia/INIT_FLAGS.class... processing com/qualcomm/vuforia/VuforiaConstants.class... processing com/qualcomm/vuforia/VideoMode.class... processing com/qualcomm/vuforia/DataSet.class... processing com/qualcomm/vuforia/VIDEO_BACKGROUND_REFLECTION.class... processing com/qualcomm/vuforia/TrackableResult$STATUS.class... processing com/qualcomm/vuforia/WordResult.class... processing com/qualcomm/vuforia/Word.class... processing com/qualcomm/vuforia/Tool.class... processing com/qualcomm/vuforia/CylinderTargetResult.class... processing com/qualcomm/vuforia/MarkerTracker.class... processing com/qualcomm/vuforia/VirtualButtonResult.class... processing com/qualcomm/vuforia/Area.class... processing com/qualcomm/vuforia/TextTracker.class... processing com/qualcomm/vuforia/CameraDevice.class... processing com/qualcomm/vuforia/VideoBackgroundTextureInfo.class... processing com/qualcomm/vuforia/VuforiaJNI.class... processing com/qualcomm/vuforia/MarkerResult.class... processing com/qualcomm/vuforia/TargetSearchResult.class... processing com/qualcomm/vuforia/ImageTracker.class... processing com/qualcomm/vuforia/Tracker.class... processing com/qualcomm/vuforia/Frame.class... processing com/qualcomm/vuforia/ImageTargetResult.class... processing com/qualcomm/vuforia/Vec2F.class... processing com/qualcomm/vuforia/Marker$MARKER_TYPE.class... processing com/qualcomm/vuforia/TrackerManager.class... processing com/qualcomm/vuforia/CameraCalibration.class... processing com/qualcomm/vuforia/Vec4F.class... processing com/qualcomm/vuforia/Vec4I.class... processing com/qualcomm/vuforia/WordList$STORAGE_TYPE.class... processing com/qualcomm/vuforia/TargetFinder.class... processing com/qualcomm/vuforia/Area$TYPE.class... processing com/qualcomm/vuforia/CameraDevice$MODE.class... processing com/qualcomm/vuforia/WordList$FILTER_MODE.class... processing com/qualcomm/vuforia/State.class... processing com/qualcomm/vuforia/CameraDevice$FOCUS_MODE.class... processing com/qualcomm/vuforia/Renderer.class... processing com/qualcomm/vuforia/UpdateCallback.class... processing com/qualcomm/vuforia/ImageTargetBuilder$FRAME_QUALITY.class... processing com/qualcomm/vuforia/HINT.class... processing com/qualcomm/vuforia/Matrix34F.class... processing com/qualcomm/vuforia/Rectangle.class... processing com/qualcomm/vuforia/Vec3F.class... processing com/qualcomm/vuforia/NonCopyable.class... processing com/qualcomm/vuforia/ImageTarget.class... processing com/qualcomm/vuforia/Marker.class... processing com/qualcomm/vuforia/Vec2I.class... processing com/qualcomm/vuforia/MultiTarget.class... processing com/qualcomm/vuforia/Trackable.class... processing com/qualcomm/vuforia/TrackableResult.class... processing com/qualcomm/vuforia/Image.class... processing com/qualcomm/QCAR/BuildConfig.class... ]

Do you have any idea how to fix this?