Android Debug Tracing problem

Question

I am testing my code in device and it is running fine. But as soon as I am adding Debug.startMethodTracing("PlaceLocator"); and Debug.stopMethodTracing(); , it is giving problem. As per log, problem is-

03-25 17:39:43.124: INFO/dalvikvm(5971): TRACE STARTED: '/sdcard/LineGraph.trace' 8192KB
03-25 17:39:43.124: ERROR/dalvikvm(5971): Unable to open trace file '/sdcard/LineGraph.trace': Permission denied
03-25 17:39:43.124: DEBUG/dalvikvm(5971): +++ active profiler count now 0
03-25 17:39:43.124: DEBUG/AndroidRuntime(5971): Shutting down VM
03-25 17:39:43.124: WARN/dalvikvm(5971): threadid=3: thread exiting with uncaught exception (group=0x4001b170)
03-25 17:39:43.124: ERROR/AndroidRuntime(5971): Uncaught handler: thread main exiting due to uncaught exception
03-25 17:39:43.131: ERROR/AndroidRuntime(5971): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android.placeLocator/com.android.placeLocator.PlaceLocator}: java.lang.RuntimeException: file open failed

Here I like to mention that I have added <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> in the manifest so that system can write file in sd card. Where is the problem?