The CMS features that were rolled into SharePoint have their fair share of issues. Working with one of my recent customers, we found a number of errors in the ULS logs in their farm. The follow errors fit into the two following categories. Although these messages seem scary, they’re just informational in nature.
If the message starts as “While initializing navigation, found Area placeholder but object was not found at: /SITES/SITECOLLECTION/SUBSITE”, it means that the currently logged in user is not a member of that sub site.
If the message starts as “While initializing navigation, found Page placeholder but object was not found at: /SITES/SITECOLLECTION/page.aspx”, it means that the page is either in “checked out” state or it’s not a publishing page.
If you don’t want to see these messages anymore, change the logging level for the Publishing category to something higher than Unexpected.