Math.sin(Math.PI)

It's a circular pre-loader. When I add the "SecondHalf" the preloader doesn't work and gives an error saying the script is causing the flash player to run slowly. How can I fix this?

This code is in:  _root.first_mc._second_mc

previewImage.onLoadProgress = function(targetMC, lBytes, tBytes) {

//FirstHalf

//This works only without "SecondHalf"

          percentDone=Math.round((lBytes / tBytes) * 100);

          _root.loaderPsnt_tx.percentDisplay.text = percentDone + "%";

//SecondHalf

//This is not working

      _root.mc_mask.clear();

      _root.mc_mask.beginFill(0xff0000, 100);

      _root.mc_mask.lineStyle(1, 0xff0000, 80);

      for (i=0; i>=c; i--) {

         x = Math.sin(Math.PI/90*i)*mask_ra;

         y = Math.cos(Math.PI/90*i)*mask_ra;

         _root.mc_mask.lineTo(x, y);

       }

      _root.mc_mask.endFill();

      c = Math.round(percentDone * (-1.84));

};

previewImage.onLoadStart = function(targetMC) {

          _root.loaderPsnt_tx._visible = _root.circle._visible = _root.mc_mask._visible = true;

          _root.circle.setMask(_root.mc_mask);

          var mask_ra:Number = (_root.circle._width / 1) * -1;

          var c:Number = 0;

          var percentDone:Number = 0;

}; 

previewImage.onLoadComplete = function(targetMC) {

          _root.loaderPsnt_tx._visible = _root.circle._visible = _root.mc_mask._visible = false;

};