Oracle database connection - error while opening connection

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C#

Oracle

connection

I am working on bulk upload functionality for that I have used Oracle.DataAccess and created connection, till last week it was working fine but now suddenly I am getting error "System.NullReferenceException: Object reference not set to an instance of an object." when i am trying to open connection using connection object. e.g. connObject.Open. I have copied code snippet below.

What I have tried:

public bool WriteToServer(string qualifiedDBName, DataTable dataTable)
    {
        OracleConnection objOracleCon = null;
        try
        {
            string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["OracleConnection"].ToString();
            objOracleCon = new OracleConnection(connectionString);
            if (objOracleCon != null)
            {
                if (objOracleCon.State == ConnectionState.Closed)
                {
                    objOracleCon.Open();
                }
                using (OracleBulkCopy bulkCopy = new OracleBulkCopy(objOracleCon))
                {
                    bulkCopy.BatchSize = 100000;
                    bulkCopy.BulkCopyTimeout = 20000;
                    bulkCopy.DestinationTableName = qualifiedDBName;
                    bulkCopy.WriteToServer(dataTable);
                    bulkCopy.Close();
                    bulkCopy.Dispose();
                    objOracleCon.Dispose();
                }
            }
        }
        catch (Exception exc)
        {
            return false;
        }
        finally
        {
            if (objOracleCon.State == ConnectionState.Open)
            {
                objOracleCon.Close();
            }
        }
        return true;
    }