Quoting "Christopher M. Jones" cjones@partialflow.com:
These aren't errors but warnings, and they generally aren't serious. You, or your host, should adjust the php error reporting settings to make these go away.
This is a debatable response. Drupal sets the error reporting to report these warnings because they should not happen. Yes, these warnings could be from badly coded contrib modules.
-- Earnie http://r-feed.com Make a Drupal difference and review core patches.