When you open a page in SharePoint designer it complains that there is a conflict and that the placeholder for the master page is missing.
This occurs when a user modifies a master page. The master page no longer contains that objects that the derived page expects, so SharePoint Designer gives an error (note that SharePoint will still recover gracefully from this, so some users simply switch between valid and invalid master pages instead of addressing the problem directly.
User used SharePoint designer to delete or comment out a placeholder.
Use CSS or mark the server control with the visible=false attribute to hide the placeholder in question.
Ulysses Ludwig is a SharePoint architect with over 16 years in the IT and computer industry. Ulysses' primary focus is SharePoint but he dabbles in the latest web technologies and likes to develop software in his spare time.