title: Drupal 7.23 warning and error messages when open page
body: <p>Drupal 7.23 When I open page (as anonymous user), I periodically get warning and error messages. The duplicate of header logo appears in the end  of page, right above error messages.
  I can't understand conditions when appears this warning &amp; error, but it seems it appears when I open page as anonymous user. Then after logging in, logging out, no any errors shown anymore.</p>
  
  <p>warning:</p>
  
  <blockquote>
    <p>Warning: Cannot modify header information - headers already sent by
    (output started at
    /home/ztiw7851207/public_html/includes/common.inc:2700) in
    drupal_send_headers() (line 1220 of
    /home/ztiw7851207/public_html/includes/bootstrap.inc).</p>
    
    <p>Warning: Cannot modify header information - headers already sent by
    (output started at
    /home/ztiw7851207/public_html/includes/common.inc:2700) in
    drupal_send_headers() (line 1216 of
    /home/ztiw7851207/public_html/includes/bootstrap.inc).</p>
  </blockquote>
  
  <p>error:</p>
  
  <blockquote>
    <p>PDOException: SQLSTATE[23000]: Integrity constraint violation: 1062
    Duplicate entry '' for key 'title': INSERT INTO {aggregator_feed}
    (fid, url, link, description, image, hash, etag, modified) VALUES
    (:db_insert_placeholder_0, :db_insert_placeholder_1,
    :db_insert_placeholder_2, :db_insert_placeholder_3,
    :db_insert_placeholder_4, :db_insert_placeholder_5,
    :db_insert_placeholder_6, :db_insert_placeholder_7); Array (
    [:db_insert_placeholder_0] => 9 [:db_insert_placeholder_1] =>
    <a href="http://hitech.com/rss/reviews/" rel="nofollow">http://hitech.com/rss/reviews/</a> [:db_insert_placeholder_2] =>
    <a href="http://hitech.com/reviews/" rel="nofollow">http://hitech.com/reviews/</a> [:db_insert_placeholder_3] => News, reviews
    and opinion outlet with obsessive coverage of cutting edge gadgets,
    consumer electronics and the science and technology they're built
    upon. [:db_insert_placeholder_4] =>
    <a href="http://hitech.com/img/rss_cover.png" rel="nofollow">http://hitech.com/img/rss_cover.png</a> [:db_insert_placeholder_5] =>
    1d37c01e3b1346cc3ac3dbf1280c3fd236c3f3433e1d44a4902066a9f3d87cbe
    [:db_insert_placeholder_6] => [:db_insert_placeholder_7] => 0 ) in
    aggregator_refresh() (line 640 of
    /home/ztiw7851207/public_html/modules/aggregator/aggregator.module).</p>
  </blockquote>
  
  <p>How to solve this issues?</p>