I am getting 401 UNAUTHORIZED when I replace the mysite15.master file with custom one.
I am logged in with administrator but still having unauthorized access when I open then SharePoint site
please make sure, that every file which is linked in the masterpage (css, pictures...) is minimum in version 1.0. (Checkin as Major Version).
I've struggled a lot with 401 unauthorized exception in masterpages. You have to find out, which file is not published.