Error when using ActivityManager.RunningTaskInfo

I am running android 2.1 and wants to get currently running apps, after running following code I am getting error: The application has stopped unexpectedly

ActivityManager mgr = (ActivityManager)context.getSystemService(ACTIVITY_SERVICE);
List<Ac开发者_Python百科tivityManager.RunningTaskInfo> tasks = mgr.getRunningTasks(100);   //error

Pls help.

---

Add the GET_TASKS permission to your manifest.