Value not inserting in DateTime column using Entity Framework - sql

Question

I am trying to insert value in DateTime column with Entity Framework but it throwing error on db.SaveChanges() function. There are 2 DateTime columns but exception throwing for only one (entry.OT_Date) with no maximum detail.
var entry = new OT_Request_N();
entry.Emp_ID = StaticFunctions.WindowUserId;
entry.slno = db.OT_Request_N.Max(x=>x.slno)+1;
entry.OT_Date= otD;
entry.OT_Time_Req = hourRequest;
entry.Remarks_Req = sError.ReqRemarks;
entry.Req_Sent_On = DateTime.Now;
entry.Supervisor_ID = sError.ManagerID;
entry.Approve_Status = 0;
db.OT_Request_N.Add(entry);
db.SaveChanges();
Here is SQL table Design
Here is class generated in edmx file
public partial class OT_Request_N
{
public int slno { get; set; }
public string Emp_ID { get; set; }
public Nullable<System.DateTime> Req_Sent_On { get; set; }
public Nullable<int> OT_Time_Req { get; set; }
public string Supervisor_ID { get; set; }
public string Remarks_Req { get; set; }
public string Remarks_App { get; set; }
public Nullable<int> OT_Time_App { get; set; }
public string Approved_By { get; set; }
public Nullable<int> Approve_Status { get; set; }
public Nullable<System.DateTime> Approved_On { get; set; }
public Nullable<int> Operations { get; set; }
public string AltReq_ID { get; set; }
public Nullable<bool> Is_alert_sent { get; set; }
public Nullable<System.DateTime> OT_Date { get; set; }
}