title: SqlBulkCopy - Unexpected existing transaction
body: <p>I am using <code>SqlBulkCopy</code> to insert large amount of data:</p>
  
  <pre><code>try
  {
     using (var bulkCopy = new SqlBulkCopy(connection))
     {
        connection.Open();
  
        using (var tran = connection.BeginTransaction(IsolationLevel.ReadCommitted))
        {
            bulkCopy.DestinationTableName = "table";
  
            bulkCopy.ColumnMappings.Add("...", "...");                            
  
            using (var dataReader = new ObjectDataReader&lt;MyObject&gt;(data))
            {
                bulkCopy.WriteToServer(dataReader);
            }
  
            tran.Commit();
            return true;
        }
     }
  }
  catch (Exception ex)
  {
      return false;
  }
  </code></pre>
  
  <p>But I always get exception:</p>
  
  <pre><code>Unexpected existing transaction.
  </code></pre>
  
  <p>Why this exception happens?</p>