DataSet does not support System.Nullable<>. + ASP>NET?

[salamaths]

This code was working fine b4 but all of a sudden it does work when i debug the application i got error i.eataSet does not support System.Nullable<>.
Plz help i have added the code below i can view data in dataset
error is after the for loor ends. i hve mentioned at the line where error is generated







protected void Page_Load(object sender, EventArgs e)
{


IList<Schedulling> Atte = new List<Schedulling>();
ReportDocument r = new ReportDocument();
Schedulling sch = new Schedulling();

sch.StrClassCodeId = Request.QueryString["classcode"];
sch.Intid = Convert.ToInt16(Request.QueryString["scheduleid"]);

DataSet dsrpt = Cosmo.DAL.Schedullings.AttendenceList(sch);

if (dsrpt.Tables[0].Rows.Count == 0)
{

}
else
{
int add = 0;


foreach (DataRow dr in dsrpt.Tables[0].Rows)
{
Schedulling rpthv = new Schedulling();
if (dr["SubjName"] != DBNull.Value)
rpthv.StrSubjName = Convert.ToString(dr["SubjName"]);
if (dr["SubjCode"] != DBNull.Value)
rpthv.StrSubjCd = Convert.ToString(dr["SubjCode"]);
if (dr["classCode"] != DBNull.Value)
rpthv.StrClassCodeId = Convert.ToString(dr["classCode"]);
if (dr["EmpName"] != DBNull.Value)
rpthv.StrEmpName = Convert.ToString(dr["EmpName"]);// Get Lecturer Name
if (dr["Days"] != DBNull.Value)
rpthv.StrDay = Convert.ToString(dr["Days"]);
if (dr["Times"] != DBNull.Value)
rpthv.StrTime = Convert.ToString(dr["Times"]);
if (dr["SName"] != DBNull.Value)
rpthv.StrLName = Convert.ToString(dr["SName"]); // Get Student NAme
if (dr["SICPassPortNo"] != DBNull.Value)
rpthv.StrGroupNo = Convert.ToString(dr["SICPassPortNo"]); //Get Ic/Passport Number
//if (dr["SMobileNo"] != DBNull.Value)
//rpthv.StrSMobileNo = Convert.ToString(dr["SMobileNo"]);// Get Mobile Num
if (dr["VenueCode"] != DBNull.Value)
rpthv.StrRoomUsage = Convert.ToString(dr["VenueCode"]); // Get Venue Code
Atte.Add(rpthv);
}

r.Load(Server.MapPath("RptAttendenceNew.rpt"));
r.SetDataSource(Atte); // Errror is generated at this line (DataSet does not support System.Nullable<>.)
r.ExportToHttpResponse(ExportFormatType.PortableDocFormat, Response, false, "AllCenterRpt");

CrystalReportViewer1.ReportSource = r;
CrystalReportViewer1.DataBind();
}
}
}


Thanks Alot
Salamath Sharieff