The ‘Insufficient Privileges’ error message in Google Sites often means there’s an item embedded on the page that you don’t have permission to view. The site’s permissions can be set differently from any embedded items within the site -- including content from other Google products like Google Calendar and Google Docs.
If you think embedded content is causing the error, you may want to try contacting an owner or editor of the embedded content. That person needs to share access to the embedded content with your Google Account. Here’s how to adjust the sharing permissions in a couple of Google products:
Of course, it’s also possible that nothing’s gone wrong and that the site owner has intentionally restricted your access.