Application built for API 8 does not work with API 7 - what goes wrong?

问题

Hey guys I simply want to downgrade my api level 8 to 7 so that i can run the application both on 2.2 and 2.1 devices. The application is running perfectly fine on 2.2 and is having problem working on 2.1

I have done changes in manifest.xml and project -> properties

My application basically uses sax parser , facebook sdk , twitter connect

This is the log cat:

03-05 12:32:13.553: WARN/dalvikvm(232): threadid=3: thread exiting with uncaught exception (group=0x4001b188)
03-05 12:32:13.563: ERROR/AndroidRuntime(232): Uncaught handler: thread main exiting due to uncaught exception
03-05 12:32:13.623: ERROR/AndroidRuntime(232): java.lang.NullPointerException
03-05 12:32:13.623: ERROR/AndroidRuntime(232):     at com.test.activity.MyActivity$FetchTopMusic.onPostExecute(MusicScreen.java:161)
03-05 12:32:13.623: ERROR/AndroidRuntime(232):     at com.test.activity.MyActivity$FetchTopMusic.onPostExecute(MusicScreen.java:1)
03-05 12:32:13.623: ERROR/AndroidRuntime(232):     at android.os.AsyncTask.finish(AsyncTask.java:417)
03-05 12:32:13.623: ERROR/AndroidRuntime(232):     at android.os.AsyncTask.access$300(AsyncTask.java:127)
03-05 12:32:13.623: ERROR/AndroidRuntime(232):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:429)
03-05 12:32:13.623: ERROR/AndroidRuntime(232):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-05 12:32:13.623: ERROR/AndroidRuntime(232):     at android.os.Looper.loop(Looper.java:123)
03-05 12:32:13.623: ERROR/AndroidRuntime(232):     at android.app.ActivityThread.main(ActivityThread.java:4363)
03-05 12:32:13.623: ERROR/AndroidRuntime(232):     at java.lang.reflect.Method.invokeNative(Native Method)
03-05 12:32:13.623: ERROR/AndroidRuntime(232):     at java.lang.reflect.Method.invoke(Method.java:521)
03-05 12:32:13.623: ERROR/AndroidRuntime(232):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
03-05 12:32:13.623: ERROR/AndroidRuntime(232):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
03-05 12:32:13.623: ERROR/AndroidRuntime(232):     at dalvik.system.NativeStart.main(Native Method)

And i get this message after the splash screen. Music Screen has async task which is calling various classes in various packages for parsing the xml content. Is this a problem in xml parser??

The line 161 is :- for (int i = 0; i < tracks.size(); i++)

Where tracks is an arrayList and all this code is working fine in 2.2