I get the following error while trying to open RiftGG:


This means RiftGG hasn't been closed and you are trying to open it again. Please, bare in mind that when you close RiftGG it will be minimize in hidden icons so it is not really closed. If you want to close RiftGG, you will have to use the "hidden icons" area and right click on the icon of RiftGG so you can see the option to close the tool.