HTC no longer supports the HTC Sync Manager program earlier than 2016.
I agree that it is necessary to make sure that the latest HTC software for the mobile phone and for the computer are installed.
Unfortunately just by using the Microsoft "uninstall" facility the files within subfolders are often left behind. These earlier files left behind in the HTC Folder on your C drive need to be manually removed after the Microsoft uninstall has been run as the old files left behind interfere with the new installation.
To do this the easiest way to find all the files and folders in your C drive is to press the Windows + E which will take you to the C directory.
You will need to find the HTC folder which on most occasions is located in the Programs Files folder. When you find the HTC folder double click on it and check if there are any subfolders or files left behind in the HTC folder or anu subfolder . All subfolders and files must be removed by highlighting the folder and hitting the delete button before you install the new version of HTC Sync Manager. Some files are difficult to remove from the HTC folder. If this occurs you need to right click on the folder then the file and change the folder extension from say ".exe" to".XXX" . By changing the file extension the computer will not recognise any files with a ".XXX" extension. You will then need to restart your computer again and then go back into the HTC folder and you should be able to click on each of the folders with the.XXX extension and delete them. By following these procedures you remove all traces of the earlier program.
Once these old folders have been deleted you should not have any problem in downloading and installing the current install a program "setup_3.1.84.4_htc_NO_EULA.exe". After installation of the new program immobile will be recognised and for security purposes HTC allocates a new unique code each time you backup or restore