Data source is an invalid type. It must be either an IListSource, IEnumerable, or IDataSource.

Does this work?

protected override void CreateChildControls()
{
        SPSite site = SPContext.Current.Site;
        SPWeb web = SPContext.Current.Web;
        SPQuery query = new SPQuery();
        SPList list1 = web.Lists.TryGetList("Vendor");
        if list1 != null)
        {
                DataTable dtvendor = new DataTable();
                dtvendor = list1.GetItems(query).GetDataTable();
                drpList.DataSource = dtvendor;
                drpList.DataTextField = "Company";
                drpList.DataValueField = "ID";
                drpList.DataBind();
                Controls.Add(drpList);
                drpList.SelectedIndexChanged += new EventHandler(this.ddlAllLists_SelectedIndexChanged);
         }
}

Good Luck!

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Alex