Searching using Javascript in Desktop App

Hi All, 

I have a desktop application which has a full built in JavaScript interface and I am trying to get a list of clients (objects) from M-Files using the API

The code I have is: 

var szFilter = "CHA"
var scValueListItem = new ActiveXObject("MFilesAPI.SearchCondition")
scValueListItem.Expression.SetValueListItemExpression(2,0);
scValueListItem.ConditionType = 9
scValueListItem.TypedValue.SetValue(1, szFilter)

var arrSearchConditions = new ActiveXObject("MFilesAPI.SearchConditions")
arrSearchConditions.Add(-1, scValueListItem)

I can only late bind to the COM API so do not have access to the types in the root API so have substituted with values. 

The line it is falling down on is scValueListItem.Expression.SetValueListItemExpression(2,0); and giving me an error of Type mismatch

Any ideas what could be causing this and what I need to do to correct it? 

Many thanks