This works in AS2, please help me get it to work in AS3

Question

I have code for a collapsing menu in actionscript 2:
counter=menu_num;
if (counter == 1) {
     while (Number(counter)<6) {
          counter = Number(counter)+1;
          setProperty("tocAni.tocMov.menu"+counter, _y, getProperty("tocAni.tocMov.menu"+counter, _y)-65);
} else if (counter == 2) {
     while (Number(counter)<6) {
          counter = Number(counter)+1;
          setProperty("tocAni.tocMov.menu"+counter, _y, getProperty("tocAni.tocMov.menu"+counter, _y)-140);
} else if (counter == 3) {
     while (Number(counter)<6) {
          counter = Number(counter)+1;
          setProperty("tocAni.tocMov.menu"+counter, _y, getProperty("tocAni.tocMov.menu"+counter, _y)-125);
} else if (counter == 4) {
     while (Number(counter)<6) {
          counter = Number(counter)+1;
          setProperty("tocAni.tocMov.menu"+counter, _y, getProperty("tocAni.tocMov.menu"+counter, _y)-85);
} else if (counter == 5) {
     while (Number(counter)<6) {
          counter = Number(counter)+1;
          setProperty("tocAni.tocMov.menu"+counter, _y, getProperty("tocAni.tocMov.menu"+counter, _y)-85);
I have this code on frame 2 in my main timeline and the same code on frame 3 that gives positive values to the variable amounts, (Frame 2 is up Frame 3 is down)... I have 6 menu movies named sequentially that contain a main link and various amounts of sublinks, (the reason there are different variable values assigned). When you click any of the main links it calls to one of the frames on the main time line, sets the variable menu_num to the menu being clicked, (i.e.. clicking menu movie one main link sets menu_num variable to 1) and moves all the menu movies below the clicked main link up or down the value indicated in the line matching the correct counter value.
I have attempted to rewrite this code this way:
var counter:Number=menu_num;
if (counter==1) {
    while (Number(counter)<6) {
        counter=Number(counter)+1;
        tocAni.tocMov.menu+counter.y,tocAni.tocMov.menu+counter.y-65;
} else if (counter == 2) {
    while (Number(counter)<6) {
        counter=Number(counter)+1;
        tocAni.tocMov.menu+counter.y,tocAni.tocMov.menu+counter.y-140;
} else if (counter == 3) {
    while (Number(counter)<6) {
        counter=Number(counter)+1;
        tocAni.tocMov.menu+counter.y,tocAni.tocMov.menu+counter.y-125;
} else if (counter == 4) {
    while (Number(counter)<6) {
        counter=Number(counter)+1;
        tocAni.tocMov.menu+counter.y,tocAni.tocMov.menu+counter.y-85;
} else if (counter == 5) {
    while (Number(counter)<6) {
        counter=Number(counter)+1;
        tocAni.tocMov.menu+counter.y,tocAni.tocMov.menu+counter.y-85;
I receive this error code when publishing in strict mode: (I receive multiples of the error, but I will only include the first)
Location - course, Layer 'tocAction', Frame 4, Line 5
Description - 1119: Access of possibly undefined property y through a reference with static type Number.
Source - tocAni.tocMov.menu+counter.y,tocAni.tocMov.menu+counter.y-65;
This is the script being used on the main link for down: (the main link is called downBT, on frame label down I have the up button)
//Listener
downBT.addEventListener(MouseEvent.CLICK, clickDownBT);
//Function
function clickDownBT(evt:MouseEvent):void {
    root.menu_num="1";
    var callDown:Function = Object["root.down"] as Function;
    gotoAndStop("down");
Any help is greatly appreciated.
A working example of this in AS2 can be found here... http://webresent.com/projectSamples/training/CBTsample/index.htm

Answer 1

assuming all your variables are defined:
counter=menu_num;
if (counter == 1) {
     while (Number(counter)<6) { // you shouldn't need to cast counter or, if you do, do it in the first line only
          counter = Number(counter)+1;  // this can be shortened to counter++;
tocAni.tocMov.["menu"+counter].y-=65;
} else if (counter == 2) {
     while (Number(counter)<6) {
          counter = Number(counter)+1;
tocAni.tocMov.["menu"+counter].y-=140;
} else if (counter == 3) {
     while (Number(counter)<6) {
          counter = Number(counter)+1;
tocAni.tocMov.["menu"+counter].y-=125;
} else if (counter == 4) {
     while (Number(counter)<6) {
          counter = Number(counter)+1;
     tocAni.tocMov.["menu"+counter].y-=85;
} else if (counter == 5) {
     while (Number(counter)<6) {
          counter = Number(counter)+1;
          tocAni.tocMov.["menu"+counter].y-=85;