Invalid cast exception was unhandled by user code - asp.net

Question

public ClientApp_Detail GetHomeDetbyClientID_AppID(string clientid, long appId)
{
ClientApp_Detail sp = null;
using (HelpDeskDataContext HDDC = Conn.GetContext())
{
sp = (from st in HDDC.ClientApp_Details where st.ClientID == clientid && st.AppID == Convert.ToInt64(appId) && st.IsDeleted != 1 select st).FirstOrDefault();
}
return sp;
}
For the above .net code i am getting the exception i.e invalid cast exception was unhandled by user code.
but all the values are of exact datatypes i.e. st.ClientID and clientid are varchar(50) and string respectively,AppId ,appid are longint IsDeleted is bit,then what is the cause of error please recommend anything regarding this if any queries i am eager to send the details.
Thank you.
[global::System.Data.Linq.Mapping.TableAttribute(Name="dbo.ClientApp_Details")]
public partial class ClientApp_Detail : INotifyPropertyChanging, INotifyPropertyChanged
{
private static PropertyChangingEventArgs emptyChangingEventArgs = new PropertyChangingEventArgs(String.Empty);
private string _ClientID;
private long _AppID;
private string _ProjectScope;
private string _ProjectStatus;
private System.DateTime _StrDt;
private System.DateTime _EndDt;
private double _NoofHours;
private long _ID;
private System.Data.Linq.Binary _TimeStamp;
//sumanth edit
private bool _IsDeleted;
private System.Nullable<System.DateTime> _CreationDt;
#region Extensibility Method Definitions
partial void OnLoaded();
partial void OnValidate(System.Data.Linq.ChangeAction action);
partial void OnCreated();
partial void OnClientIDChanging(string value);
partial void OnClientIDChanged();
partial void OnAppIDChanging(long value);
partial void OnAppIDChanged();
partial void OnProjectScopeChanging(string value);
partial void OnProjectScopeChanged();
partial void OnProjectStatusChanging(string value);
partial void OnProjectStatusChanged();
partial void OnStrDtChanging(System.DateTime value);
partial void OnStrDtChanged();
partial void OnEndDtChanging(System.DateTime value);
partial void OnEndDtChanged();
partial void OnNoofHoursChanging(double value);
partial void OnNoofHoursChanged();
partial void OnIDChanging(long value);
partial void OnIDChanged();
partial void OnTimeStampChanging(System.Data.Linq.Binary value);
partial void OnTimeStampChanged();
partial void OnIsDeletedChanging(bool value);
partial void OnIsDeletedChanged();
partial void OnCreationDtChanging(System.Nullable<System.DateTime> value);
partial void OnCreationDtChanged();
#endregion
public ClientApp_Detail()
{
OnCreated();
}
[global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_ClientID", DbType="VarChar(50) NOT NULL", CanBeNull=false, UpdateCheck=UpdateCheck.Never)]
public string ClientID
{
get
{
return this._ClientID;
}
set
{
if ((this._ClientID != value))
{
this.OnClientIDChanging(value);
this.SendPropertyChanging();
this._ClientID = value;
this.SendPropertyChanged("ClientID");
this.OnClientIDChanged();
}
}
}
[global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_AppID", DbType="BigInt NOT NULL", UpdateCheck=UpdateCheck.Never)]
public long AppID
{
get
{
return this._AppID;
}
set
{
if ((this._AppID != value))
{
this.OnAppIDChanging(value);
this.SendPropertyChanging();
this._AppID = value;
this.SendPropertyChanged("AppID");
this.OnAppIDChanged();
}
}
}
[global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_ProjectScope", DbType="Text", UpdateCheck=UpdateCheck.Never)]
public string ProjectScope
{
get
{
return this._ProjectScope;
}
set
{
if ((this._ProjectScope != value))
{
this.OnProjectScopeChanging(value);
this.SendPropertyChanging();
this._ProjectScope = value;
this.SendPropertyChanged("ProjectScope");
this.OnProjectScopeChanged();
}
}
}
[global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_ProjectStatus", DbType="Text", UpdateCheck=UpdateCheck.Never)]
public string ProjectStatus
{
get
{
return this._ProjectStatus;
}
set
{
if ((this._ProjectStatus != value))
{
this.OnProjectStatusChanging(value);
this.SendPropertyChanging();
this._ProjectStatus = value;
this.SendPropertyChanged("ProjectStatus");
this.OnProjectStatusChanged();
}
}
}
[global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_StrDt", DbType="DateTime NOT NULL", UpdateCheck=UpdateCheck.Never)]
public System.DateTime StrDt
{
get
{
return this._StrDt;
}
set
{
if ((this._StrDt != value))
{
this.OnStrDtChanging(value);
this.SendPropertyChanging();
this._StrDt = value;
this.SendPropertyChanged("StrDt");
this.OnStrDtChanged();
}
}
}
[global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_EndDt", DbType="DateTime NOT NULL", UpdateCheck=UpdateCheck.Never)]
public System.DateTime EndDt
{
get
{
return this._EndDt;
}
set
{
if ((this._EndDt != value))
{
this.OnEndDtChanging(value);
this.SendPropertyChanging();
this._EndDt = value;
this.SendPropertyChanged("EndDt");
this.OnEndDtChanged();
}
}
}
[global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_NoofHours", DbType="Float NOT NULL", UpdateCheck=UpdateCheck.Never)]
public double NoofHours
{
get
{
return this._NoofHours;
}
set
{
if ((this._NoofHours != value))
{
this.OnNoofHoursChanging(value);
this.SendPropertyChanging();
this._NoofHours = value;
this.SendPropertyChanged("NoofHours");
this.OnNoofHoursChanged();
}
}
}
[global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_ID", AutoSync=AutoSync.OnInsert, DbType="BigInt NOT NULL IDENTITY", IsPrimaryKey=true, IsDbGenerated=true, UpdateCheck=UpdateCheck.Never)]
public long ID
{
get
{
return this._ID;
}
set
{
if ((this._ID != value))
{
this.OnIDChanging(value);
this.SendPropertyChanging();
this._ID = value;
this.SendPropertyChanged("ID");
this.OnIDChanged();
}
}
}
[global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_TimeStamp", AutoSync=AutoSync.Always, DbType="rowversion NOT NULL", CanBeNull=false, IsDbGenerated=true, IsVersion=true, UpdateCheck=UpdateCheck.Never)]
public System.Data.Linq.Binary TimeStamp
{
get
{
return this._TimeStamp;
}
set
{
if ((this._TimeStamp != value))
{
this.OnTimeStampChanging(value);
this.SendPropertyChanging();
this._TimeStamp = value;
this.SendPropertyChanged("TimeStamp");
this.OnTimeStampChanged();
}
}
}
[global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_IsDeleted", DbType="Bit NOT NULL", UpdateCheck=UpdateCheck.Never)]
public bool IsDeleted
{
get
{
return this._IsDeleted;
}
set
{
if ((this._IsDeleted != value))
{
this.OnIsDeletedChanging(value);
this.SendPropertyChanging();
this._IsDeleted = value;
this.SendPropertyChanged("IsDeleted");
this.OnIsDeletedChanged();
}
}
}