Unable to open trace file

08-30 11:40:49.274: ERROR/dalvikvm(280): Unable to open trace file '/sdcard/x.trace': Permission denied
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="junluo.DebugTest"
      android:versionCode="1"
      android:versionName="1.0">
    <uses-sdk android:minSdkVersion="8" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".DebugTestActivity"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>    </application>
</manifest>    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        Debug.startMethodTracing("x");      
    }
    
    @Override
    public void onDestroy() {
     super.onDestroy();
     Debug.stopMethodTracing();    }  Window → Preferences → Android → Launch 設置了sdcard文件。