If you are experiencing issues with the installer, it is possible to manually install Age of the Ring 5.1.
1. Create a folder named Age of the Ring 5.1 in an installation location of your choice (e.g C:/Program Files/Age of the Ring 5.1).
2. Open the aotr.zip included in the downloaded AotR_Version_5.1.rar and extract all of its contents into the folder you have created.
3. Create a shortcut from the lotrbfme2ep1.exe file in your vanilla RotWK folder
4. Go into the shortcut's properties and edit the Target box so that at the end of "C:\Program Files (x86)\Electronic Arts\The Lord of the Rings, The Rise of the Witch-king\lotrbfme2ep1.exe" there is -mod "location of your aotr folder inside Age of the Ring 5.1"
e.g. "C:\Program Files (x86)\Electronic Arts\The Lord of the Rings, The Rise of the Witch-king\lotrbfme2ep1.exe" -mod "C:\Program Files\Age of the Ring 5.1\aotr"
5. Click apply and close the shortcut's properties. You can now launch Age of the Ring 5.1 from that shortcut.