@(Html.Infragistics().Combo().ID("controlID")
                            .TextKey("Text")
                            .ValueKey("Key")
                            .SelectedIndexes(new [] {0})
                            .DataSourceUrl(Url.Action("Datasource", "Combo"))
                            .Render())

When I run it on IE8,  there will be a javascript error: 'undefined' is null or not a object. By the way, it works fine on firefox.

This error occurs in _dataChange function because this._dataSource is 'undefined':

_dataChange: function (q, z) {
            var l, H, F, E, m, G, s, t, r, w, k, A = this._lodWait,
                B = 1,
                u = -1,
                j = -1,
                D = this._needsSel,
                v = -1,
                y = this._keyVal,
                x = this._key,
                n = this._itemsHolder,
                p = this._dataSource,
                C = this.options;

Do you have any ieas?