Your request to http://192.168.1.101/spotnshare/subscribe.php is failing and returning a non-JSON string (probably a PHP error). You can print out the value with a
Log.i("tagconvertstr", "["+result+"]");
before the new JSONObject
call to see what you’re getting before parsing it.
EDIT: if you are using Eclipse you can set a break point and step through to see what’s going on.