Catryna, when you click on the + sign, add libraries icon, poser should open an explorer window (in windows, I assume it does the equivalent on a Mac). Navigate in this to the folder actually called runtime, not the folder that contains the runtime, select this and click on open. Poser should now add the library with the name of the folder containing the runtime folder. Poser only cares about 2 things as far as I'm aware, one is that the folder is called runtime and the other is that it has permission to write to it, so in later versions of windows don't have the runtimes in your programs files, best to have them in the public folders