Following Import References are required in using section for Creating SSRS Report user Control in Enterprise portal axapta
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.DataVisualization.Charting;
using System.Web.UI.WebControls;
using Microsoft.Dynamics.Framework.Portal.UI.WebControls;
using Microsoft.Dynamics.Framework.Portal.UI.WebControls.WebParts;
using System.Diagnostics;
using Microsoft.Dynamics.AX.Framework.Reporting.Shared;
using Microsoft.Dynamics.Framework.BusinessConnector.Session;
using Microsoft.Dynamics.AX.Framework.Portal.Data;
using Microsoft.Dynamics.Framework.Portal.CommonControls;
using System.Globalization;
using Microsoft.Dynamics.AX.Framework.Services.Client;
using Microsoft.Dynamics.Framework.Portal;
using Microsoft.Dynamics.Framework.Portal.UI;
using Proxy = Microsoft.Dynamics.Framework.BusinessConnector.Proxy;
using Microsoft.Dynamics.Framework.BusinessConnector.Adapter;
using System.Security.Principal;