This error happens when the page name is in use. 
  1. Navigate to Site Explorer>Pages & Templates
  2. Click the Search tab and search for the page name you want to use
    • If the page is returned
      1. Click the hand icon to edit page properties
      2. Update the page name
      3. Click Save
    • If the page is not returned
      1. From Site Explorer>Pages & Templates, select the Deleted Pages/Templates folder
      2. Search through the pages to see if the page name is found
      3. If it is found, either delete the page or restore the page and change its name