ArgumentError: Error #1063 issue

This is usually a simple error, yet I cannot find an obvious answer.

The full error is: 'ArgumentError: Error #1063: Argument count mismatch on com::previewSelection/selectionOn(). Expected 2, got 1.'

The obvious issue is that I'm only giving 1 bit of information and not 2, however I am definitely giving 2.

Main code:

   function previewOn(e){
        previewTile2.selectionOn(holdBar_mc, area1_mc);
        previewTile2.removeEventListener(MouseEvent.CLICK, previewOn);
        previewTile2.addEventListener(MouseEvent.CLICK, previewOff);
        stage.setChildIndex(previews, 1);
        var editOpen:Tween = new Tween(editTab, 'x', Strong.easeOut, editTab.x, -215, 1, true);
        createTiles();

    }

And the class file function:

public开发者_运维问答 function selectionOn(holdBar:MovieClip, area1:MovieClip){
            holdBarDown = new Tween(holdBar, 'y', Strong.easeOut, holdBar.y, 518, 1, true);
            area1Up = new Tween(area1, 'y', Strong.easeOut, area1.y, area1.y - 300, 1, true);
        }

Neither holdBar_mc or area1_mc are 'null' when traced.

The file runs without issue or slow-down, yet the Argument error constantly returns. Any ideas?