title: facebook unity sdk 6.0 crash app at second login
body: <p>Created a simple app with facebook unity sdk 6.0. </p>
  
  <p>In start function call the init facebook.</p>
  
  <p>There is a button call login and the login callback just output string.</p>
  
  <p>Run on a Samsung galaxy s5 with android 4.4.2.</p>
  
  <p>Issue (100% repeatable):</p>
  
  <pre><code> 1. First time click login button, get the facebook login screen.
   2. Click exit button, back to app.
   3. Click login button again, app crashed.
  </code></pre>
  
  <p>Crash dump:</p>
  
  <pre><code>W/dalvikvm(16020): threadid=1: thread exiting with uncaught exception (group=0x417f3da0)
  V/SmartFaceService - 3rd party pause(  704): onReceive [android.intent.action.ACTIVITY_STATE/com.xxxxx.testfacebook/create]
  I/SpenGestureManager(  704): setFocusWindow21055
  D/PointerIcon(  704): setMouseIconStyle1 pointerType: 1001iconType:101 flag:0
  D/PointerIcon(  704): setMouseCustomIcon IconType is same.101
  D/PointerIcon(  704): setHoveringSpenIconStyle1 pointerType: 10001iconType:1 flag:0
  D/PointerIcon(  704): setHoveringSpenCustomIcon IconType is same.1
  E/AndroidRuntime(16020): FATAL EXCEPTION: main
  E/AndroidRuntime(16020): Process: com.xxxxx.testfacebook, PID: 16020
  E/AndroidRuntime(16020): java.lang.Error: FATAL EXCEPTION [main]
  E/AndroidRuntime(16020): Unity version     : 4.5.3f3
  E/AndroidRuntime(16020): Device model      : samsung SAMSUNG-SM-G900A
  E/AndroidRuntime(16020): Device fingerprint: samsung/klteuc/klteatt:4.4.2/KOT49H/G900AUCU1ANCE:user/release-keys
  E/AndroidRuntime(16020): 
  E/AndroidRuntime(16020): Caused by: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.xxxxx.testfacebook/com.facebook.unity.FBUnityLoginActivity}: java.lang.UnsupportedOperationException: Session: an attempt was made to open an already opened session.
  E/AndroidRuntime(16020):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2328)
  E/AndroidRuntime(16020):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2386)
  E/AndroidRuntime(16020):    at android.app.ActivityThread.access$900(ActivityThread.java:169)
  E/AndroidRuntime(16020):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1277)
  E/AndroidRuntime(16020):    at android.os.Handler.dispatchMessage(Handler.java:102)
  E/AndroidRuntime(16020):    at android.os.Looper.loop(Looper.java:136)
  E/AndroidRuntime(16020):    at android.app.ActivityThread.main(ActivityThread.java:5476)
  E/AndroidRuntime(16020):    at java.lang.reflect.Method.invokeNative(Native Method)
  E/AndroidRuntime(16020):    at java.lang.reflect.Method.invoke(Method.java:515)
  E/AndroidRuntime(16020):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268)
  E/AndroidRuntime(16020):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084)
  E/AndroidRuntime(16020):    at dalvik.system.NativeStart.main(Native Method)
  E/AndroidRuntime(16020): Caused by: java.lang.UnsupportedOperationException: Session: an attempt was made to open an already opened session.
  E/AndroidRuntime(16020):    at com.facebook.Session.open(Session.java:1223)
  E/AndroidRuntime(16020):    at com.facebook.Session.openForPublish(Session.java:519)
  E/AndroidRuntime(16020):    at com.facebook.unity.FBLogin.sessionOpenRequest(FBLogin.java:113)
  E/AndroidRuntime(16020):    at com.facebook.unity.FBLogin.login(FBLogin.java:98)
  E/AndroidRuntime(16020):    at com.facebook.unity.FBUnityLoginActivity.onCreate(FBUnityLoginActivity.java:14)
  E/AndroidRuntime(16020):    at android.app.Activity.performCreate(Activity.java:5451)
  E/AndroidRuntime(16020):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1093)
  E/AndroidRuntime(16020):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2292)
  E/AndroidRuntime(16020):    ... 11 more
  W/ActivityManager(  704):   Force finishing activity com.xxxxx.testfacebook/com.facebook.unity.FBUnityLoginActivity
  I/SQLiteSecureOpenHelper(27856): getWritableDatabase(pwd)
  I/SQLiteSecureOpenHelper(27856): getDatabaseLocked(b,b,pwd)...
  W/ActivityManager(  704):   Force finishing activity com.xxxxx.testfacebook/com.unity3d.player.UnityPlayerNativeActivity
  V/SmartFaceService - 3rd party pause(  704): onReceive [android.intent.action.ACTIVITY_STATE/com.xxxxx.testfacebook/pause]
  I/dumpstate(16164): begin
  I/SpenGestureManager(  704): setFocusWindow0
  D/EnterpriseDeviceManager(  704): ContainerId: 0
  D/PointerIcon(  704): setMouseIconStyle1 pointerType: 1001iconType:101 flag:0
  D/PointerIcon(  704): setMouseCustomIcon IconType is same.101
  D/PointerIcon(  704): setHoveringSpenIconStyle1 pointerType: 10001iconType:1 flag:0
  D/CrashAnrDetector(  704): processName: com.xxxxx.testfacebook
  D/PointerIcon(  704): setHoveringSpenCustomIcon IconType is same.1
  D/CrashAnrDetector(  704): broadcastEvent : com.xxxxx.testfacebook data_app_crash
  </code></pre>