You may have faced this message when you tried to edit a SharePoint 2010 site’s master page:
Master page editing has been disabled for this site. Contact the site collection administrator to request permission.
This is caused in 2 cases: first case if the site collection administrator has stopped the permission to edit the master pages for the site collection, so if you are a site collection administator go to site settings, and under site collection administration you can see the button “sharepoint designer settings”, make sure that customizing master pages is enabled, if its disabled and you can’t do something about it, then this is case 2 : it’s disabled from the web application itself, so now you have to go to your web application settings using central administration tool, and on the general application settings tab, choose sharepoint designer settings, and enable the same option.
Note: Site owners can’t edit master pages unless site collection admin allow the feature, and site collection admins can’t allow it unless farm admin allow it at the web application itself.