No user on Windows is guaranteed to never get an access denied error. While the Administrator account and members of the Administrator group normally are given full access to pretty much everything, ACLs can still be set on files (and registry) entries that deny them read, write, delete, and other kinds of permissions. The only special power the admin accounts have is take ownership of files and change the permissions of files. While being able to change the permissions ultimately gives an admin account ful control over the system, most applications, including installers, won't try to force things by changing permissions when they get accessed denied errors.
There's really nothing you can do fix this other than ensuring no ACL on the system will ever deny an admin access. This is basically what the script in the MSDN blog linked above tries to do.