I get an error message when installing the software:
This means you are not installing the software as administrator, you have to give permission to install the software.
If you did and the issue still persist, could be that your anti-virus is blocking the installation. Please, deactivate the antivirus you have and try to install again the tool.
Warning!: If your antivirus blocks the installation of RiftGG will block the match data too. So if you want to get data from Riot, you will have to deactivate it or add RiftGG to the whitelist of the antivirus.