track.scrobble issue in Android

iam writing code for last.fm in android.
As i was trying to scrobble using url =
http://ws.audioscrobbler.com/2.0/?method=track.scrobble&timestamp=1328162314&api_key=xxxxxxx&api_sig=xxxxxxx&sk=xxxxxxxx&album=xxxxxx&track=xxxxx&artist=xxxxxxx
it gives me response code as : 403.
OR
<?xml version="1.0" encoding="utf-8"?>
<lfm status="failed">
<error code="3">Invalid Method - No method with that name in this package</error></lfm>
as i have used request type as post, but then also it is not giving me proper response.
pls give me suggestion to solve this problem that iam facing in android.

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i have also made post request to the root url using Rest Client addon of Firefox browser.
eg: http://ws.audioscrobbler.com/2.0/
With all parameters (including the 'method') sent in the POST body.
eg:?method=track.scrobble&timestamp=1328186610&api_key=xxxxxxxx&api_sig=31005047a68cd77fc25d7cf0654962f9&sk=xxxxxx
&album=Recovery&track=NotAfraid&artist=Eminem

then also iam geting response as:
<error code="3">Invalid Method - No method with that name in this package</error>

here authtoken and api_signature is calculated as :
authToken = MD5.getHashString("xxxxxxx" + MD5.getHashString("xxxxxxxx"));
api_sig = MD5.getHashString("album"+album+"api_key"+api_key+
"artist"+artist+
"authToken"+authToken+"methodtrack.scrobble"+
"sk"+sk+
"timestamp"+timestamp+
"track"+track+
secret);