What version of Flash are you using?
If above MX... ActionScript is case sensitive.
a couple things to mention:
1.) onClpiEvent(enterFrame)() is not a good way of coding.. you should NOT put code ON or IN movieClips on the stage. You 'should' put your code in FRAMES in the MAIN timeline.
so:
onClipEvent (enterFrame)():
should be more like:
someClip.onEnterFrame = function(){};
2.) all mentions/reference of _root should be converted to relative paths/scope (ie: this, this._parent, _parent...etc)
3.) case sensitive.... this where I believe YOUR problem lies..
math.round should be Math.round()..
Code:
onClipEvent (enterFrame) {
tb = Math.round(_root.container.getBytesTotal()/1024);
lb = Math.round(_root.container.getBytesLoaded()/1024);
if (tb>0 && lb>0) {
this.percent = Math.round((lb/tb)*100);
this.gotoAndPlay(this.percent);
if (lb>=tb) {
_root.transition.gotoAndPlay("out");
_root.preloader.gotoAndStop("stop");
}
}
}
4.) I suggest looking into using the MovieClipLoader() class.. it it is VERY (very) useful for triggering actions when content is loaded as well as providing data for any preloder. 
update:
here is a quick example of how to use the MovieClipLoader() class..
simplified version:
PHP Code:
// create our MovieClipLoader instance (called: contentLoader)
var contentLoader:MovieClipLoader = new MovieClipLoader();
//create an object to handle the data available form the MovieClipLoader() object.
var contentListener:Object = new Object();
// create function that fires/executes when the content starts loading
contentListener.onLoadStart = function(target_mc:MovieClip):Void {
trace(">> contentListener.onLoadStart()");
}
// create function that fires/executes each time a byte/potion is loaded (preloader)
contentListener.onLoadProgress = function(target_mc:MovieClip, bytesLoaded:Number, bytesTotal:Number):Void {
trace(">> contentListener.onLoadProgress()");
}
// create function that fires/executes when the content is complete
contentListener.onLoadComplete = function(target_mc:MovieClip, httpStatus:Number):Void {
trace(">> contentListener.onLoadComplete()");
};
// create function that fires/executes when the content has initialized and is ready for manipulation
contentListener.onLoadInit = function(target_mc:MovieClip):Void {
trace(">> contentListener.onLoadInit()");
};
// add our 'listener' object to our MovieClipLoader instance
contentLoader.addListener(contentListener);
// create an empty movieClip on the stage to hold our content...(this can be any target you want though)
var containerClip:MovieClip = this.createEmptyMovieClip("containerClip", this.getNextHighestDepth());
// finally, make the call to load whatever content we want.. this is just an on-line image (but can be whatever, .swf, .jpg, clips in library..etc)
contentLoader.loadClip("someIMage.jpgg", containerClip);
PHP Code:
//create an object to handle the data available form the MovieClipLoader() object.
var contentListener:Object = new Object();
// create function that fires/executes when the content is complete
contentListener.onLoadProgress = function(target_mc:MovieClip, bytesLoaded:Number, bytesTotal:Number):Void {
trace(target_mc._name + ".onLoadProgress with " + bytesLoaded + " bytes of " + bytesTotal);
trace(">> Invoked every time the loading content is written to the hard disk during the loading process (that is, between MovieClipLoader.onLoadStart and MovieClipLoader.onLoadComplete).");
}
// create function that fires/executes when the content is complete
contentListener.onLoadComplete = function(target_mc:MovieClip, httpStatus:Number):Void {
trace(">> contentListener.onLoadComplete()");
trace(">> =============================");
trace(">> "+target_mc._name+"._width: " + target_mc._width);
trace(">>> {its 0 because the content hasnt (although complete) hasnt initiliazed and Flash can not access any properties.}");
trace(newline);
};
// create function that fires/executes when the content has initialized and is ready for manipulation
contentListener.onLoadInit = function(target_mc:MovieClip):Void {
trace(">> contentListener.onLoadInit()");
trace(">> =============================");
trace(">> "+target_mc._name+"._width: " + target_mc._width);
trace(">>> {its 315 because once the content/clip has initialized, Flash can not access its properties.}");
trace(newline);
// Draw outline around the loaded content
target_mc._x = Stage.width/2-target_mc._width/2;
target_mc._y = Stage.height/2-target_mc._width/2;
var w:Number = target_mc._width;
var h:Number = target_mc._height;
target_mc.lineStyle(4, 0x000000);
target_mc.moveTo(0, 0);
target_mc.lineTo(w, 0);
target_mc.lineTo(w, h);
target_mc.lineTo(0, h);
target_mc.lineTo(0, 0);
target_mc._rotation = 0;
};
// create our MovieClipLoader instance (called: contentLoader)
var contentLoader:MovieClipLoader = new MovieClipLoader();
// add our 'listener' object to our MovieClipLoader instance
contentLoader.addListener(contentListener);
// create an empty movieClip on the stage to hold our content...(this can be any target you want though)
var containerClip:MovieClip = this.createEmptyMovieClip("containerClip", this.getNextHighestDepth());
// finally, make the call to load whatever content we want.. this is just an on-line image (but can be whatever, .swf, .jpg, clips in library..etc)
contentLoader.loadClip("http://www.w3.org/Icons/w3c_main.png", containerClip);