I must be missing something here (sendvars question)

I have some sendvars code that works just fine if I launch the swf locally, but as soon as I upload it to the web, the process no longer works. I wondered if it was a security issue with CS3 since the same code worked until we upgraded recently.

function trackActivity(actLbl){

	_root.test.text='tracking...'

	if ( (_root.t == 'y') || (_root.t == undefined)) {

		save_check=new LoadVars();

		sendVars = new LoadVars();

		sendVars.ac=actLbl;

			if (_root.tag!=undefined){

				sendVars.ac += _root.tag;

			}		sendVars.fl=_root.fl

		sendVars.to=_root.to

		sendVars.fr=_root.fr

		save_check.onLoad = function(){

			if (save_check.response=="passed"){

				_root.test.text='done... ';

			} else {

				_root.test.text='problem...';				

			}

		}

		_root.test.text='sending: ' + sendVars.ac + 'n' + sendVars.to + 'n' + sendVars.fr;

		sendVars.sendAndLoad("http://domain.com/track.php", save_check,"POST");

	}

}

t=y

to=100

fr=50

tag=0

trackActivity('test')

any ideas?