public void UserOnlineDelete()
{
         DateTime timeNow = DateTime.Now;
	string timeNowString = timeNow.AddMinutes(- 15 ).ToString( "yyyy-MM-dd hh:mm:ss" );
	try
	{	
		FirebirdSql.Data.Firebird.FbConnection con = new FbConnection(ConnStr);
		con.Open();

		FirebirdSql.Data.Firebird.FbTransaction myTransaction = con.BeginTransaction();
		FirebirdSql.Data.Firebird.FbCommand ConnCommand = new FbCommand( "DELETE_ONLINE_USER" , con, myTransaction);
		ConnCommand.CommandType = CommandType.StoredProcedure;

		FirebirdSql.Data.Firebird.FbParameter mytime = new FbParameter( "TIMENOW" , FbType.VarChar);
		mytime.Value = timeNowString;
		ConnCommand.Parameters.Add(mytime);

		ConnCommand.ExecuteNonQuery();
		myTransaction.Commit();
		con.Close();
	}
	catch
	{
	}
}// end of function