Some time back, I created a now-locked thread (
https://www.tweaking.com/forums/index.php/topic,6083.0.html) with a temporary resolution for installing the Tweaking tool by booting into safe mode to accomplish that task successfully, but as the workaround wouldn't enable my Acronis TrueImage app to install in safe mode I had not completed a backup; that changed earlier today and the resolution may help someone else with comparable installation problems.
This started when I had become frustrated with the various "help" offerings through MS or most of the other sites which were identified in searches on the original error message, and life intervened in the form of chores and weather to distract me until this morning. A new update for Skype today wouldn't install in a similar manner, but presented a different style and form of error message ("Access is denied" referencing "error 5") -- another search with the combination brought up many of the same threads and posts as earlier, but also one reference to the MS KB article linked below, which revealed the problem lay somewhere in the permissions for vital folders being "read-only" as the installation process requires writing to such a folder. The solution is to select the critical TEMP folders and toggle the top folder's properties "read-only" feature on and off, choosing the option to apply the action to all files and folders below; one may be under the root drive C:\ and the other under the relevant Windows\USERS\***\AppData\Local\Temp path.
https://support.microsoft.com/en-us/help/2623670/access-denied-or-other-errors-when-you-access-or-work-with-files-and-fAfter I took that action for both folder lines and rebooted, I re-attempted the Skype update; it ran through fine, so I launched the TrueImage installation again and it ran through to completion. Once I got the product activated and an initial backup performed, I went to their user forum to report the method of fixing the related installation errors and have now come here to report on the resolution. I'll have to wait to test it against a new release of the Tweaking tool, and will report the outcome at that point in an update to this post if it remains unlocked.