Make sure that the variables were sent

How can i make sure that the variables were sent to the .php script and afther that to proced to the next step ?

I know that the variables arrive (by watching the php sessions), but i want to be sure that the variables arrived and afther that to go to the next frame

var myVar = -1;

loadVars.load("someurl");

onEnterFrame = function()
{
if (myVar != -1)
{
delete onEnterFrame;
gotoAndPlay(nextFrame);
}
}
stop();