Crystal report prompting for login on export everytime in ASP.Net

When I export my report from an aspx page using crystal report viewer I am prompted for a login everytime. (This only happens on export, not on load.) I'm using Visual Studio 2012 and SAP Crystal Reports 13.0.15.xxx.

Enter Values The report you requested requires further information.

I have tried setting EnableDatabaseLogonPromt to False, but that generates this error:

"Method not found: 'CrystalDecisions.ReportAppServer.DataDefModel.ProperyBag...."

I think with my code is correct because the report loads into a new aspx page and receives data. But when I want to export my report or print it, I face that popup. I am using MSSQL SERVER 2012 AS DBMS so I don't need any username or password to log in. How can I correct this?

MY CODE IS HERE

protected void Page_Load(object sender, EventArgs e)
{
  if (!IsPostBack)
  {
    var x = Server.MapPath("~");
    int CustomersId = Convert.ToInt32(Request.QueryString["CustomersID"]);

    CustomersiDataSet Customersi = new CustomersiDataSet();
    CustomersiDataSet.CustomersiTableDataTable CustomersiDT = new CustomersiDataSet.CustomersiTableDataTable();

    var Customers = DA.Data.Services.DACustomersi.GetByCustomersId(CustomersId);

    CustomersiDT.AddCustomersiTableRow(Customers.Name, Customers.LastName, Customers.IDNumber.ToString());
    Customersi.Tables["CustomersiTable"].Merge(CustomersiDT);

    ReportDocument ReportCustomers = new rpt_Customersi();       
    ReportCustomers.SetDataSource(Customersi);

    CrystalReportViewer1.ReportSource = ReportCustomers;

    //I ALSO TRIED WITH CACHING REPORT BUT THAT I AM FACING AGAIN ISSUE : MethodNotFound:"...."             
    // //Cache["Report"] = ReportCustomers;
    // ReportCustomers .ExportToHttpResponse(CrystalDecisions.Shared.ExportFormatType.PortableDocFormat, Response, true, "MyCustomers");
  }
}