argument error #2068: Invalid sound

Hi,

I'm trying to use the static variables and methods for the first time.

So I took the code, I had previously on an upper level component, down to the related class file.

Its all working fine, but the sound does not want to play.

Gives the error: Invalid sound. The row is marked bold.

What is causing that error?

Many thanks in advance!

private static var numberForFlowerSound: uint = 0;

private static var flowerSound01: BellLoop01Multitrack = new BellLoop01Multitrack();

private static var flowerSound02: BellLoop02Multitrack = new BellLoop02Multitrack();

private static var flowerSound03: BellLoop03Multitrack = new BellLoop03Multitrack();

private static var flowerSound04: BellLoop04Multitrack = new BellLoop04Multitrack();

private static function countForFlowersSound(): void

     {

            numberForFlowerSound++;

       if (numberForFlowerSound == 1)

       {

          flowerSound01.play();

       }

     else if (numberForFlowerSound == 2)

       {

            flowerSound02.play();

       }

       else if (numberForFlowerSound == 3)

        {

            flowerSound03.play();

       }

       else if (numberForFlowerSound == 4)

       {

            flowerSound04.play();

            numberForFlowerSound = 0;

       }

  }