The installer displays a 'Windows cannot access the specified device, path or file' error.
You will see this error message if you are trying to install Defraggler without being logged in as an administrator:
Solution: Log in as an administrator and then run the installation program, or contact your system administrator for assistance.
Alternative solution: Use Defraggler Portable which you have installed on a USB drive using another computer. It may have limited functionality if you are not using an administrator account.