I'm running El Capitan in Mac Pro 3,1 8-core @3.2GHz with Elsa GTX680 in PCIe slot #1 but Web Driver would not install. It always produces an error message at the end of the installation process and when I open System Preference, the NVIDIA Driver Manager preference pane is visible at the bottom but a click on the icon only produces an error message that says "Please install again". Similarly the Cuda driver also produces an error message at the end of its installation process but Photoshop CC is showing GTX680 as GPU in its preference panel and SETI@Home in Boinc Manager is working as screen saver. Before installing the drivers I have all security software turned off and access privilege sorted out by TechTool Pro but this happens only on my external startup SSD and I have no problem with my internal SSD. I'm wondering what's going on and if anyone think of a possible cause, an input will be appreciated. Is it okay to have Cuda driver alone running?